Image encoding/decoding method and device, and recording medium having bitstream stored therein

ABSTRACT

An image encoding/decoding method and apparatus for performing representative sample-based intra prediction are provided. An image decoding method may comprise deriving an intra prediction mode of a current block, configuring a reference sample of the current block, and performing intra prediction for the current block based on the intra prediction mode and the reference sample, wherein the intra prediction is representative sample-based prediction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 16/755,962, filed on Apr. 14, 2020, which is a U.S.National Stage Application of International Application No.PCT/KR2018/012310, filed on Oct. 18, 2018, which claims the benefitunder 35 USC 119(a) and 365(b) of Korean Patent Application No.10-2017-0135124, filed on Oct. 18, 2017 and Korean Patent ApplicationNo. 10-2018-0109320, filed on Sep. 13, 2018, in the Korean IntellectualProperty Office.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding an image and a recording medium storing a bitstream.Particularly, the present invention relates to a method and apparatusfor encoding/decoding an image using intra prediction and a recordingmedium storing a bitstream generated by an image encodingmethod/apparatus of the present invention.

BACKGROUND ART

Recently, demands for high-resolution and high-quality images such ashigh definition (HD) images and ultra high definition (UHD) images, haveincreased in various application fields. However, higher resolution andquality image data has increasing amounts of data in comparison withconventional image data. Therefore, when transmitting image data byusing a medium such as conventional wired and wireless broadbandnetworks, or when storing image data by using a conventional storagemedium, costs of transmitting and storing increase. In order to solvethese problems occurring with an increase in resolution and quality ofimage data, high-efficiency image encoding/decoding techniques arerequired for higher-resolution and higher-quality images.

Image compression technology includes various techniques, including: aninter-prediction technique of predicting a pixel value included in acurrent picture from a previous or subsequent picture of the currentpicture; an intra-prediction technique of predicting a pixel valueincluded in a current picture by using pixel information in the currentpicture; a transform and quantization technique for compressing energyof a residual signal; an entropy encoding technique of assigning a shortcode to a value with a high appearance frequency and assigning a longcode to a value with a low appearance frequency; etc. Image data may beeffectively compressed by using such image compression technology, andmay be transmitted or stored.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusfor encoding and decoding an image to enhance compression efficiency.

Another object of the present invention is to provide a method andapparatus for encoding and decoding an image using intra prediction toenhance compression efficiency.

Another object of the present invention is to provide a recording mediumstoring a bitstream generated by an image encoding method/apparatus ofthe present invention.

Technical Solution

An image decoding method according to an embodiment of the presentinvention may comprise deriving an intra prediction mode of a currentblock, configuring a reference sample of the current block, andperforming intra prediction for the current block based on the intraprediction mode and the reference sample, wherein the intra predictionmay be representative sample-based prediction.

In the image decoding method according to the present invention, therepresentative sample-based prediction may comprise determining aposition of the representative sample, determining a value of therepresentative sample, and predicting a sample in the current blockusing the representative sample and the reference sample.

In the image decoding method according to the present invention, theposition of the representative sample may be determined as apredetermined fixed position or determined by information signaledthrough a bitstream.

In the image decoding method according to the present invention, thepredetermined fixed position may be a right-bottom position of thecurrent block.

In the image decoding method according to the present invention, thevalue of the representative sample may be determined as a statisticvalue using the representative sample specified by the position of therepresentative sample and a neighboring sample of the representativesample.

In the image decoding method according to the present invention, theposition of the representative sample may be a right-bottom position ofthe current block, and the value of the representative sample may be anaverage value of the representative sample, a left sample of therepresentative sample, a left-upper sample of the representative sampleand an upper sample of the representative sample.

In the image decoding method according to the present invention, thedetermining the value of the representative sample may comprise derivinga prediction value for the representative sample, reconstructing aresidual value for the representative sample, and determining the valueof the representative sample using the prediction value and the residualvalue.

In the image decoding method according to the present invention, theprediction value for the representative sample may be derived using aleft reference sample of the current block and an upper reference sampleof the current block.

In the image decoding method according to the present invention, aprediction value for a right boundary sample in the current blockadjacent to a right boundary of the current block may be derived usinginterpolation of the representative sample and the upper referencesample, and a prediction value for a bottom boundary sample in thecurrent block adjacent to a bottom boundary of the current block may bederived using interpolation of the representative sample and the leftreference sample.

In the image decoding method according to the present invention, aprediction value for a sample in the current block may be derived usinginterpolation of the right boundary sample, the bottom boundary sample,the upper reference sample and the left reference sample.

An image encoding method according to another embodiment of the presentinvention may comprises determining an intra prediction mode of acurrent block, configuring a reference sample of the current block, andperforming intra prediction for the current block based on the intraprediction mode and the reference sample, wherein the intra predictionmay be representative sample-based prediction.

In the image encoding method according to the present invention, therepresentative sample-based prediction may comprise determining aposition of the representative sample, determining a value of therepresentative sample, and predicting a sample in the current blockusing the representative sample and the reference sample.

In the image encoding method according to the present invention, theposition of the representative sample may be determined as apredetermined fixed position or encoded by information signaled througha bitstream.

In the image encoding method according to the present invention, thevalue of the representative sample may be determined as a statisticvalue using the representative sample specified by the position of therepresentative sample and a neighboring sample of the representativesample.

In the image encoding method according to the present invention, theposition of the representative sample may be a right-bottom position ofthe current block, and the value of the representative sample may be anaverage value of the representative sample, a left sample of therepresentative sample, a left-upper sample of the representative sampleand an upper sample of the representative sample.

In the image encoding method according to the present invention, thedetermining the value of the representative sample may comprise derivinga prediction value for the representative sample, deriving a residualvalue for the representative sample, and determining the value of therepresentative sample using the prediction value and the residual value.

In the image encoding method according to the present invention, theprediction value for the representative sample may be derived using aleft reference sample of the current block and an upper reference sampleof the current block.

In the image encoding method according to the present invention, aprediction value for a right boundary sample in the current blockadjacent to a right boundary of the current block may be derived usinginterpolation of the representative sample and the upper referencesample, and a prediction value for a bottom boundary sample in thecurrent block adjacent to a bottom boundary of the current block may bederived using interpolation of the representative sample and the leftreference sample.

In the image encoding method according to the present invention, aprediction value for a sample in the current block may be derived usinginterpolation of the right boundary sample, the bottom boundary sample,the upper reference sample and the left reference sample.

A computer readable recording medium according to another embodiment ofthe present invention may store a bitstream generated by an imageencoding method or apparatus according to the present invention.

Advantageous Effects

According to the present invention, a method and apparatus for encodingand decoding an image to enhance compression efficiency may be provided.

According to the present invention, a method and apparatus for encodingand decoding an image using intra prediction to enhance compressionefficiency may be provided.

According to the present invention, a recording medium storing abitstream generated by an image encoding method/apparatus of the presentinvention may be provided.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing configurations of an encodingapparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing configurations of a decoding apparatusaccording to an embodiment of the present invention.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image.

FIG. 4 is a view for explaining an embodiment of a process of intraprediction.

FIG. 5 is a view for explaining intra prediction according to thepresent invention.

FIG. 6 is an exemplary diagram illustrating the relationship between aluma block and a chroma block.

FIG. 7 is a diagram for describing a plurality of reconstructed samplelines.

FIG. 8 is a diagram for describing a process of replacing an unavailablesample with an available sample.

FIGS. 9A-9D illustrate various filter shapes.

FIGS. 10A-10D are diagrams describing intra prediction according to theshapes of the current block.

FIG. 11 is a diagram for describing neighboring samples of a currentblock used to derive a parameter of linear models which are used forpredicting a chroma component from a luma component.

FIGS. 12A-B show exemplary diagrams illustrating a process ofrestructuring a color component block.

FIGS. 13A-13E are diagrams illustrating an embodiment performingrestructuring by using a plurality of upper-side reference sample linesand/or a plurality of left-side reference sample lines.

FIGS. 14A-14D are exemplary diagrams illustrating reference samples usedfor the restructuring in accordance with an intra prediction mode or acoding parameter of a corresponding block.

FIGS. 15A-15G are diagrams illustrating an exemplary restructured firstcolor component corresponding block when a second color componentprediction target block is a 4×4 block.

FIG. 16 is a diagram illustrating a sample of a first color componentand a sample of a second color component.

FIGS. 17A-17D are diagrams illustrating an exemplary method ofdetermining a representative sample.

FIG. 18 is a diagram illustrating an exemplary method of performingprediction for a representative sample.

FIGS. 19A-19B are diagrams illustrating another exemplary method ofperforming prediction for a representative sample.

FIG. 20 is a diagram illustrating an exemplary method of generatingright-column prediction samples and bottom-row prediction samples of thecurrent block by using the reconstructed representative sample and thereference samples.

FIG. 21 is a diagram illustrating an exemplary method of performingprediction by using the reference samples and the right-column orbottom-row prediction samples.

FIG. 22 is a diagram illustrating an exemplary prediction method for acase in which a current block is divided into sub-blocks.

MODE FOR CARRYING OUT THE INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, althoughthe exemplary embodiments can be construed as including allmodifications, equivalents, or substitutes in a technical concept and atechnical scope of the present invention. The similar reference numeralsrefer to the same or similar functions in various aspects. In thedrawings, the shapes and dimensions of elements may be exaggerated forclarity. In the following detailed description of the present invention,references are made to the accompanying drawings that show, by way ofillustration, specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to implement the present disclosure. Itshould be understood that various embodiments of the present disclosure,although different, are not necessarily mutually exclusive. For example,specific features, structures, and characteristics described herein, inconnection with one embodiment, may be implemented within otherembodiments without departing from the spirit and scope of the presentdisclosure. In addition, it should be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the spirit and scope of the presentdisclosure. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present disclosure isdefined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to what the claims claim.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

Furthermore, constitutional parts shown in the embodiments of thepresent invention are independently shown so as to representcharacteristic functions different from each other. Thus, it does notmean that each constitutional part is constituted in a constitutionalunit of separated hardware or software. In other words, eachconstitutional part includes each of enumerated constitutional parts forconvenience. Thus, at least two constitutional parts of eachconstitutional part may be combined to form one constitutional part orone constitutional part may be divided into a plurality ofconstitutional parts to perform each function. The embodiment where eachconstitutional part is combined and the embodiment where oneconstitutional part is divided are also included in the scope of thepresent invention, if not departing from the essence of the presentinvention.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded. In other words, when a specific element is referred to as being“included”, elements other than the corresponding element are notexcluded, but additional elements may be included in embodiments of thepresent invention or the scope of the present invention.

In addition, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In describingexemplary embodiments of the present invention, well-known functions orconstructions will not be described in detail since they mayunnecessarily obscure the understanding of the present invention. Thesame constituent elements in the drawings are denoted by the samereference numerals, and a repeated description of the same elements willbe omitted.

Hereinafter, an image may mean a picture configuring a video, or maymean the video itself. For example, “encoding or decoding or both of animage” may mean “encoding or decoding or both of a moving picture”, andmay mean “encoding or decoding or both of one image among images of amoving picture.”

Hereinafter, terms “moving picture” and “video” may be used as the samemeaning and be replaced with each other.

Hereinafter, a target image may be an encoding target image which is atarget of encoding and/or a decoding target image which is a target ofdecoding. Also, a target image may be an input image inputted to anencoding apparatus, and an input image inputted to a decoding apparatus.Here, a target image may have the same meaning with the current image.

Hereinafter, terms “image”, “picture, “frame” and “screen” may be usedas the same meaning and be replaced with each other.

Hereinafter, a target block may be an encoding target block which is atarget of encoding and/or a decoding target block which is a target ofdecoding. Also, a target block may be the current block which is atarget of current encoding and/or decoding. For example, terms “targetblock” and “current block” may be used as the same meaning and bereplaced with each other.

Hereinafter, terms “block” and “unit” may be used as the same meaningand be replaced with each other. Or a “block” may represent a specificunit.

Hereinafter, terms “region” and “segment” may be replaced with eachother.

Hereinafter, a specific signal may be a signal representing a specificblock. For example, an original signal may be a signal representing atarget block. A prediction signal may be a signal representing aprediction block. A residual signal may be a signal representing aresidual block.

In embodiments, each of specific information, data, flag, index, elementand attribute, etc. may have a value. A value of information, data,flag, index, element and attribute equal to “0” may represent a logicalfalse or the first predefined value. In other words, a value “0”, afalse, a logical false and the first predefined value may be replacedwith each other. A value of information, data, flag, index, element andattribute equal to “1” may represent a logical true or the secondpredefined value. In other words, a value “1”, a true, a logical trueand the second predefined value may be replaced with each other.

When a variable i or j is used for representing a column, a row or anindex, a value of i may be an integer equal to or greater than 0, orequal to or greater than 1. That is, the column, the row, the index,etc. may be counted from 0 or may be counted from 1.

Description of Terms

Encoder: means an apparatus performing encoding. That is, means anencoding apparatus.

Decoder: means an apparatus performing decoding. That is, means andecoding apparatus.

Block: is an M×N array of a sample. Herein, M and N may mean positiveintegers, and the block may mean a sample array of a two-dimensionalform. The block may refer to a unit. A current block my mean an encodingtarget block that becomes a target when encoding, or a decoding targetblock that becomes a target when decoding. In addition, the currentblock may be at least one of an encode block, a prediction block, aresidual block, and a transform block.

Sample: is a basic unit constituting a block. It may be expressed as avalue from 0 to 2^(Bd)−1 according to a bit depth (Bd). In the presentinvention, the sample may be used as a meaning of a pixel. That is, asample, a pel, a pixel may have the same meaning with each other.

Unit: may refer to an encoding and decoding unit. When encoding anddecoding an image, the unit may be a region generated by partitioning asingle image. In addition, the unit may mean a subdivided unit when asingle image is partitioned into subdivided units during encoding ordecoding. That is, an image may be partitioned into a plurality ofunits. When encoding and decoding an image, a predetermined process foreach unit may be performed. A single unit may be partitioned intosub-units that have sizes smaller than the size of the unit. Dependingon functions, the unit may mean a block, a macroblock, a coding treeunit, a code tree block, a coding unit, a coding block), a predictionunit, a prediction block, a residual unit), a residual block, atransform unit, a transform block, etc. In addition, in order todistinguish a unit from a block, the unit may include a luma componentblock, a chroma component block associated with the luma componentblock, and a syntax element of each color component block. The unit mayhave various sizes and forms, and particularly, the form of the unit maybe a two-dimensional geometrical figure such as a square shape, arectangular shape, a trapezoid shape, a triangular shape, a pentagonalshape, etc. In addition, unit information may include at least one of aunit type indicating the coding unit, the prediction unit, the transformunit, etc., and a unit size, a unit depth, a sequence of encoding anddecoding of a unit, etc.

Coding Tree Unit: is configured with a single coding tree block of aluma component Y, and two coding tree blocks related to chromacomponents Cb and Cr. In addition, it may mean that including the blocksand a syntax element of each block. Each coding tree unit may bepartitioned by using at least one of a quad-tree partitioning method, abinary-tree partitioning method, a ternary-tree partitioning method,etc. to configure a lower unit such as coding unit, prediction unit,transform unit, etc. It may be used as a term for designating a sampleblock that becomes a process unit when encoding/decoding an image as aninput image. Here, a quad-tree may mean a quarternary-tree.

When the size of a coding block falls within a first predeterminedrange, only quad-tree partitioning is allowed for the coding block.Here, the first predetermined range may be defined by at least one of amaximum size and a minimum size of a coding block that can bepartitioned only by quad-tree partitioning. Information indicating themaximum/minimum size of the coding block for which quad-treepartitioning is allowed may be signaled as data included in a bitstream,and the information may be signaled in units of at least one of asequence, a picture parameter, and a slice (segment). Alternatively, themaximum/minimum size of the coding block may be a fixed size preset inthe encoder/decoder. For example, when the size of the coding block iswithin a range from 64×64 to 256×256, the coding block can bepartitioned only by quad-tree partitioning. Alternatively, when the sizeof the coding block is larger than the maximum size of a transform block(TB), the coding block can be partitioned only by quad-treepartitioning. In this case, the block to be partitioned into quadrantsmay be either a coding block or a transform block. In this case,information (for example, split_flag) indicating the quad-treepartitioning of a coding block may be a flag indicating whether or notthe coding unit is partitioned by quad-tree partitioning. When the sizeof a coding block falls within a second predetermined range, the codingblock can be partitioned only by binary-tree partitioning orternary-tree partitioning. In this case, the above description ofquad-tree partitioning can also be applied to binary-tree partitioningor ternary-tree partitioning.

Coding Tree Block: may be used as a term for designating any one of a Ycoding tree block, Cb coding tree block, and Cr coding tree block.

Neighbor Block: may mean a block adjacent to a current block. The blockadjacent to the current block may mean a block that comes into contactwith a boundary of the current block, or a block positioned within apredetermined distance from the current block. The neighbor block maymean a block adjacent to a vertex of the current block. Herein, theblock adjacent to the vertex of the current block may mean a blockvertically adjacent to a neighbor block that is horizontally adjacent tothe current block, or a block horizontally adjacent to a neighbor blockthat is vertically adjacent to the current block.

Reconstructed Neighbor block: may mean a neighbor block adjacent to acurrent block and which has been already spatially/temporally encoded ordecoded. Herein, the reconstructed neighbor block may mean areconstructed neighbor unit. A reconstructed spatial neighbor block maybe a block within a current picture and which has been alreadyreconstructed through encoding or decoding or both. A reconstructedtemporal neighbor block is a block at a corresponding position as thecurrent block of the current picture within a reference image, or aneighbor block thereof.

Unit Depth: may mean a partitioned degree of a unit. In a treestructure, the highest node (Root Node) may correspond to the first unitwhich is not partitioned. Also, the highest node may have the leastdepth value. In this case, the highest node may have a depth of level 0.A node having a depth of level 1 may represent a unit generated bypartitioning once the first unit. A node having a depth of level 2 mayrepresent a unit generated by partitioning twice the first unit. A nodehaving a depth of level n may represent a unit generated by partitioningn-times the first unit. A Leaf Node may be the lowest node and a nodewhich cannot be partitioned further. A depth of a Leaf Node may be themaximum level. For example, a predefined value of the maximum level maybe 3. A depth of a root node may be the lowest and a depth of a leafnode may be the deepest. In addition, when a unit is expressed as a treestructure, a level in which a unit is present may mean a unit depth.

Bitstream: may mean a bitstream including encoding image information.

Parameter Set: corresponds to header information among a configurationwithin a bitstream. At least one of a video parameter set, a sequenceparameter set, a picture parameter set, and an adaptation parameter setmay be included in a parameter set. In addition, a parameter set mayinclude a slice header, and tile header information.

Parsing: may mean determination of a value of a syntax element byperforming entropy decoding, or may mean the entropy decoding itself.

Symbol: may mean at least one of a syntax element, a coding parameter,and a transform coefficient value of an encoding/decoding target unit.In addition, the symbol may mean an entropy encoding target or anentropy decoding result.

Prediction Mode: may be information indicating a mode encoded/decodedwith intra prediction or a mode encoded/decoded with inter prediction.

Prediction Unit: may mean a basic unit when performing prediction suchas inter-prediction, intra-prediction, inter-compensation,intra-compensation, and motion compensation. A single prediction unitmay be partitioned into a plurality of partitions having a smaller size,or may be partitioned into a plurality of lower prediction units. Aplurality of partitions may be a basic unit in performing prediction orcompensation. A partition which is generated by dividing a predictionunit may also be a prediction unit.

Prediction Unit Partition: may mean a form obtained by partitioning aprediction unit.

Transform Unit: may mean a basic unit when performing encoding/decodingsuch as transform, inverse-transform, quantization, dequantization,transform coefficient encoding/decoding of a residual signal. A singletransform unit may be partitioned into a plurality of lower-leveltransform units having a smaller size. Here,transformation/inverse-transformation may comprise at least one amongthe first transformation/the first inverse-transformation and the secondtransformation/the second inverse-transformation.

Scaling: may mean a process of multiplying a quantized level by afactor. A transform coefficient may be generated by scaling a quantizedlevel. The scaling also may be referred to as dequantization.

Quantization Parameter: may mean a value used when generating aquantized level using a transform coefficient during quantization. Thequantization parameter also may mean a value used when generating atransform coefficient by scaling a quantized level duringdequantization. The quantization parameter may be a value mapped on aquantization step size.

Delta Quantization Parameter: may mean a difference value between apredicted quantization parameter and a quantization parameter of anencoding/decoding target unit.

Scan: may mean a method of sequencing coefficients within a unit, ablock or a matrix. For example, changing a two-dimensional matrix ofcoefficients into a one-dimensional matrix may be referred to asscanning, and changing a one-dimensional matrix of coefficients into atwo-dimensional matrix may be referred to as scanning or inversescanning.

Transform Coefficient: may mean a coefficient value generated aftertransform is performed in an encoder. It may mean a coefficient valuegenerated after at least one of entropy decoding and dequantization isperformed in a decoder. A quantized level obtained by quantizing atransform coefficient or a residual signal, or a quantized transformcoefficient level also may fall within the meaning of the transformcoefficient.

Quantized Level: may mean a value generated by quantizing a transformcoefficient or a residual signal in an encoder. Alternatively, thequantized level may mean a value that is a dequantization target toundergo dequantization in a decoder. Similarly, a quantized transformcoefficient level that is a result of transform and quantization alsomay fall within the meaning of the quantized level.

Non-zero Transform Coefficient: may mean a transform coefficient havinga value other than zero, or a transform coefficient level or a quantizedlevel having a value other than zero.

Quantization Matrix: may mean a matrix used in a quantization process ora dequantization process performed to improve subjective or objectiveimage quality. The quantization matrix also may be referred to as ascaling list.

Quantization Matrix Coefficient: may mean each element within aquantization matrix. The quantization matrix coefficient also may bereferred to as a matrix coefficient.

Default Matrix: may mean a predetermined quantization matrixpreliminarily defined in an encoder or a decoder.

Non-default Matrix: may mean a quantization matrix that is notpreliminarily defined in an encoder or a decoder but is signaled by auser.

Statistic Value: a statistic value for at least one among a variable, anencoding parameter, a constant value, etc. which have a computablespecific value may be one or more among an average value, a weightedaverage value, a weighted sum value, the minimum value, the maximumvalue, the most frequent value, a median value, an interpolated value ofthe corresponding specific values.

FIG. 1 is a block diagram showing a configuration of an encodingapparatus according to an embodiment to which the present invention isapplied.

An encoding apparatus 100 may be an encoder, a video encoding apparatus,or an image encoding apparatus. A video may include at least one image.The encoding apparatus 100 may sequentially encode at least one image.

Referring to FIG. 1, the encoding apparatus 100 may include a motionprediction unit 111, a motion compensation unit 112, an intra-predictionunit 120, a switch 115, a subtractor 125, a transform unit 130, aquantization unit 140, an entropy encoding unit 150, a dequantizationunit 160, a inverse-transform unit 170, an adder 175, a filter unit 180,and a reference picture buffer 190.

The encoding apparatus 100 may perform encoding of an input image byusing an intra mode or an inter mode or both. In addition, encodingapparatus 100 may generate a bitstream including encoded informationthrough encoding the input image, and output the generated bitstream.The generated bitstream may be stored in a computer readable recordingmedium, or may be streamed through a wired/wireless transmission medium.When an intra mode is used as a prediction mode, the switch 115 may beswitched to an intra. Alternatively, when an inter mode is used as aprediction mode, the switch 115 may be switched to an inter mode.Herein, the intra mode may mean an intra-prediction mode, and the intermode may mean an inter-prediction mode. The encoding apparatus 100 maygenerate a prediction block for an input block of the input image. Inaddition, the encoding apparatus 100 may encode a residual block using aresidual of the input block and the prediction block after theprediction block being generated. The input image may be called as acurrent image that is a current encoding target. The input block may becalled as a current block that is current encoding target, or as anencoding target block.

When a prediction mode is an intra mode, the intra-prediction unit 120may use a sample of a block that has been already encoded/decoded and isadjacent to a current block as a reference sample. The intra-predictionunit 120 may perform spatial prediction for the current block by using areference sample, or generate prediction samples of an input block byperforming spatial prediction. Herein, the intra prediction may meanintra-prediction,

When a prediction mode is an inter mode, the motion prediction unit 111may retrieve a region that best matches with an input block from areference image when performing motion prediction, and deduce a motionvector by using the retrieved region. In this case, a search region maybe used as the region. The reference image may be stored in thereference picture buffer 190. Here, when encoding/decoding for thereference image is performed, it may be stored in the reference picturebuffer 190.

The motion compensation unit 112 may generate a prediction block byperforming motion compensation for the current block using a motionvector. Herein, inter-prediction may mean inter-prediction or motioncompensation.

When the value of the motion vector is not an integer, the motionprediction unit 111 and the motion compensation unit 112 may generatethe prediction block by applying an interpolation filter to a partialregion of the reference picture. In order to perform inter prediction ormotion compensation on a coding unit, it may be determined that whichmode among a skip mode, a merge mode, an advanced motion vectorprediction (AMVP) mode, and a current picture referring mode is used formotion prediction and motion compensation of a prediction unit includedin the corresponding coding unit. Then, inter prediction or motioncompensation may be differently performed depending on the determinedmode.

The subtractor 125 may generate a residual block by using a residual ofan input block and a prediction block. The residual block may be calledas a residual signal. The residual signal may mean a difference betweenan original signal and a prediction signal. In addition, the residualsignal may be a signal generated by transforming or quantizing, ortransforming and quantizing a difference between the original signal andthe prediction signal. The residual block may be a residual signal of ablock unit.

The transform unit 130 may generate a transform coefficient byperforming transform of a residual block, and output the generatedtransform coefficient. Herein, the transform coefficient may be acoefficient value generated by performing transform of the residualblock. When a transform skip mode is applied, the transform unit 130 mayskip transform of the residual block.

A quantized level may be generated by applying quantization to thetransform coefficient or to the residual signal. Hereinafter, thequantized level may be also called as a transform coefficient inembodiments.

The quantization unit 140 may generate a quantized level by quantizingthe transform coefficient or the residual signal according to aparameter, and output the generated quantized level. Herein, thequantization unit 140 may quantize the transform coefficient by using aquantization matrix.

The entropy encoding unit 150 may generate a bitstream by performingentropy encoding according to a probability distribution on valuescalculated by the quantization unit 140 or on coding parameter valuescalculated when performing encoding, and output the generated bitstream.The entropy encoding unit 150 may perform entropy encoding of sampleinformation of an image and information for decoding an image. Forexample, the information for decoding the image may include a syntaxelement.

When entropy encoding is applied, symbols are represented so that asmaller number of bits are assigned to a symbol having a high chance ofbeing generated and a larger number of bits are assigned to a symbolhaving a low chance of being generated, and thus, the size of bit streamfor symbols to be encoded may be decreased. The entropy encoding unit150 may use an encoding method for entropy encoding such as exponentialGolomb, context-adaptive variable length coding (CAVLC),context-adaptive binary arithmetic coding (CABAC), etc. For example, theentropy encoding unit 150 may perform entropy encoding by using avariable length coding/code (VLC) table. In addition, the entropyencoding unit 150 may deduce a binarization method of a target symboland a probability model of a target symbol/bin, and perform arithmeticcoding by using the deduced binarization method, and a context model.

In order to encode a transform coefficient level (quantized level), theentropy encoding unit 150 may change a two-dimensional block formcoefficient into a one-dimensional vector form by using a transformcoefficient scanning method.

A coding parameter may include information (flag, index, etc.) such assyntax element that is encoded in an encoder and signaled to a decoder,and information derived when performing encoding or decoding. The codingparameter may mean information required when encoding or decoding animage. For example, at least one value or a combination form of aunit/block size, a unit/block depth, unit/block partition information,unit/block shape, unit/block partition structure, whether to partitionof a quad-tree form, whether to partition of a binary-tree form, apartition direction of a binary-tree form (horizontal direction orvertical direction), a partition form of a binary-tree form (symmetricpartition or asymmetric partition), whether to partition of aternary-tree form, a partition direction of a ternary-tree form(horizontal direction or vertical direction), a partition form of aternary-tree form (symmetric partition or asymmetric partition), whetherto partition of a multi-type-tree form, a partition direction of amulti-type-tree form (horizontal direction or vertical direction), apartition form of a multi-type-tree form (symmetric partition orasymmetric partition), a partitioning tree of multi-type-tree form, aprediction mode (intra prediction or inter prediction), a lumaintra-prediction mode/direction, a chroma intra-predictionmode/direction, intra partition information, inter partitioninformation, a coding block partition flag, a prediction block partitionflag, a transform block partition flag, a reference sample filteringmethod, a reference sample filter tab, a reference sample filtercoefficient, a prediction block filtering method, a prediction blockfilter tap, a prediction block filter coefficient, a prediction blockboundary filtering method, a prediction block boundary filter tab, aprediction block boundary filter coefficient, an intra-prediction mode,an inter-prediction mode, motion information, a motion vector, a motionvector difference, a reference picture index, a inter-prediction angle,an inter-prediction indicator, a prediction list utilization flag, areference picture list, a reference picture, a motion vector predictorindex, a motion vector predictor candidate, a motion vector candidatelist, whether to use a merge mode, a merge index, a merge candidate, amerge candidate list, whether to use a skip mode, an interpolationfilter type, an interpolation filter tab, an interpolation filtercoefficient, a motion vector size, a presentation accuracy of a motionvector, a transform type, a transform size, information of whether ornot a primary (first) transform is used, information of whether or not asecondary transform is used, a primary transform index, a secondarytransform index, information of whether or not a residual signal ispresent, a coded block pattern, a coded block flag (CBF), a quantizationparameter, a quantization parameter residue, a quantization matrix,whether to apply an intra loop filter, an intra loop filter coefficient,an intra loop filter tab, an intra loop filter shape/form, whether toapply a deblocking filter, a deblocking filter coefficient, a deblockingfilter tab, a deblocking filter strength, a deblocking filtershape/form, whether to apply an adaptive sample offset, an adaptivesample offset value, an adaptive sample offset category, an adaptivesample offset type, whether to apply an adaptive loop filter, anadaptive loop filter coefficient, an adaptive loop filter tab, anadaptive loop filter shape/form, a binarization/inverse-binarizationmethod, a context model determining method, a context model updatingmethod, whether to perform a regular mode, whether to perform a bypassmode, a context bin, a bypass bin, a significant coefficient flag, alast significant coefficient flag, a coded flag for a unit of acoefficient group, a position of the last significant coefficient, aflag for whether a value of a coefficient is larger than 1, a flag forwhether a value of a coefficient is larger than 2, a flag for whether avalue of a coefficient is larger than 3, information on a remainingcoefficient value, a sign information, a reconstructed luma sample, areconstructed chroma sample, a residual luma sample, a residual chromasample, a luma transform coefficient, a chroma transform coefficient, aquantized luma level, a quantized chroma level, a transform coefficientlevel scanning method, a size of a motion vector search area at adecoder side, a shape of a motion vector search area at a decoder side,a number of time of a motion vector search at a decoder side,information on a CTU size, information on a minimum block size,information on a maximum block size, information on a maximum blockdepth, information on a minimum block depth, an imagedisplaying/outputting sequence, slice identification information, aslice type, slice partition information, tile identificationinformation, a tile type, tile partition information, a picture type, abit depth of an input sample, a bit depth of a reconstruction sample, abit depth of a residual sample, a bit depth of a transform coefficient,a bit depth of a quantized level, and information on a luma signal orinformation on a chroma signal may be included in the coding parameter.

Herein, signaling the flag or index may mean that a corresponding flagor index is entropy encoded and included in a bitstream by an encoder,and may mean that the corresponding flag or index is entropy decodedfrom a bitstream by a decoder.

When the encoding apparatus 100 performs encoding throughinter-prediction, an encoded current image may be used as a referenceimage for another image that is processed afterwards. Accordingly, theencoding apparatus 100 may reconstruct or decode the encoded currentimage, or store the reconstructed or decoded image as a reference imagein reference picture buffer 190.

A quantized level may be dequantized in the dequantization unit 160, ormay be inverse-transformed in the inverse-transform unit 170. Adequantized or inverse-transformed coefficient or both may be added witha prediction block by the adder 175. By adding the dequantized orinverse-transformed coefficient or both with the prediction block, areconstructed block may be generated. Herein, the dequantized orinverse-transformed coefficient or both may mean a coefficient on whichat least one of dequantization and inverse-transform is performed, andmay mean a reconstructed residual block.

A reconstructed block may pass through the filter unit 180. The filterunit 180 may apply at least one of a deblocking filter, a sampleadaptive offset (SAO), and an adaptive loop filter (ALF) to areconstructed sample, a reconstructed block or a reconstructed image.The filter unit 180 may be called as an in-loop filter.

The deblocking filter may remove block distortion generated inboundaries between blocks. In order to determine whether or not to applya deblocking filter, whether or not to apply a deblocking filter to acurrent block may be determined based samples included in several rowsor columns which are included in the block. When a deblocking filter isapplied to a block, another filter may be applied according to arequired deblocking filtering strength.

In order to compensate an encoding error, a proper offset value may beadded to a sample value by using a sample adaptive offset. The sampleadaptive offset may correct an offset of a deblocked image from anoriginal image by a sample unit. A method of partitioning samples of animage into a predetermined number of regions, determining a region towhich an offset is applied, and applying the offset to the determinedregion, or a method of applying an offset in consideration of edgeinformation on each sample may be used.

The adaptive loop filter may perform filtering based on a comparisonresult of the filtered reconstructed image and the original image.Samples included in an image may be partitioned into predeterminedgroups, a filter to be applied to each group may be determined, anddifferential filtering may be performed for each group. Information ofwhether or not to apply the ALF may be signaled by coding units (CUs),and a form and coefficient of the ALF to be applied to each block mayvary.

The reconstructed block or the reconstructed image having passed throughthe filter unit 180 may be stored in the reference picture buffer 190. Areconstructed block processed by the filter unit 180 may be a part of areference image. That is, a reference image is a reconstructed imagecomposed of reconstructed blocks processed by the filter unit 180. Thestored reference image may be used later in inter prediction or motioncompensation.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

A decoding apparatus 200 may a decoder, a video decoding apparatus, oran image decoding apparatus.

Referring to FIG. 2, the decoding apparatus 200 may include an entropydecoding unit 210, a dequantization unit 220, a inverse-transform unit230, an intra-prediction unit 240, a motion compensation unit 250, anadder 255, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive a bitstream output from theencoding apparatus 100. The decoding apparatus 200 may receive abitstream stored in a computer readable recording medium, or may receivea bitstream that is streamed through a wired/wireless transmissionmedium. The decoding apparatus 200 may decode the bitstream by using anintra mode or an inter mode. In addition, the decoding apparatus 200 maygenerate a reconstructed image generated through decoding or a decodedimage, and output the reconstructed image or decoded image.

When a prediction mode used when decoding is an intra mode, a switch maybe switched to an intra. Alternatively, when a prediction mode used whendecoding is an inter mode, a switch may be switched to an inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block bydecoding the input bitstream, and generate a prediction block. When thereconstructed residual block and the prediction block are obtained, thedecoding apparatus 200 may generate a reconstructed block that becomes adecoding target by adding the reconstructed residual block with theprediction block. The decoding target block may be called a currentblock.

The entropy decoding unit 210 may generate symbols by entropy decodingthe bitstream according to a probability distribution. The generatedsymbols may include a symbol of a quantized level form. Herein, anentropy decoding method may be a inverse-process of the entropy encodingmethod described above.

In order to decode a transform coefficient level (quantized level), theentropy decoding unit 210 may change a one-directional vector formcoefficient into a two-dimensional block form by using a transformcoefficient scanning method.

A quantized level may be dequantized in the dequantization unit 220, orinverse-transformed in the inverse-transform unit 230. The quantizedlevel may be a result of dequantizing or inverse-transforming or both,and may be generated as a reconstructed residual block. Herein, thedequantization unit 220 may apply a quantization matrix to the quantizedlevel.

When an intra mode is used, the intra-prediction unit 240 may generate aprediction block by performing, for the current block, spatialprediction that uses a sample value of a block adjacent to a decodingtarget block and which has been already decoded.

When an inter mode is used, the motion compensation unit 250 maygenerate a prediction block by performing, for the current block, motioncompensation that uses a motion vector and a reference image stored inthe reference picture buffer 270.

The adder 225 may generate a reconstructed block by adding thereconstructed residual block with the prediction block. The filter unit260 may apply at least one of a deblocking filter, a sample adaptiveoffset, and an adaptive loop filter to the reconstructed block orreconstructed image. The filter unit 260 may output the reconstructedimage. The reconstructed block or reconstructed image may be stored inthe reference picture buffer 270 and used when performinginter-prediction. A reconstructed block processed by the filter unit 260may be a part of a reference image. That is, a reference image is areconstructed image composed of reconstructed blocks processed by thefilter unit 260. The stored reference image may be used later in interprediction or motion compensation.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image. FIG. 3 schematically shows anexample of partitioning a single unit into a plurality of lower units.

In order to efficiently partition an image, when encoding and decoding,a coding unit (CU) may be used. The coding unit may be used as a basicunit when encoding/decoding the image. In addition, the coding unit maybe used as a unit for distinguishing an intra prediction mode and aninter prediction mode when encoding/decoding the image. The coding unitmay be a basic unit used for prediction, transform, quantization,inverse-transform, dequantization, or an encoding/decoding process of atransform coefficient.

Referring to FIG. 3, an image 300 is sequentially partitioned in alargest coding unit (LCU), and a LCU unit is determined as a partitionstructure. Herein, the LCU may be used in the same meaning as a codingtree unit (CTU). A unit partitioning may mean partitioning a blockassociated with to the unit. In block partition information, informationof a unit depth may be included. Depth information may represent anumber of times or a degree or both in which a unit is partitioned. Asingle unit may be partitioned into a plurality of lower level unitshierarchically associated with depth information based on a treestructure. In other words, a unit and a lower level unit generated bypartitioning the unit may correspond to a node and a child node of thenode, respectively. Each of partitioned lower unit may have depthinformation. Depth information may be information representing a size ofa CU, and may be stored in each CU. Unit depth represents times and/ordegrees related to partitioning a unit. Therefore, partitioninginformation of a lower-level unit may comprise information on a size ofthe lower-level unit.

A partition structure may mean a distribution of a coding unit (CU)within a CTU 310. Such a distribution may be determined according towhether or not to partition a single CU into a plurality (positiveinteger equal to or greater than 2 including 2, 4, 8, 16, etc.) of CUs.A horizontal size and a vertical size of the CU generated bypartitioning may respectively be half of a horizontal size and avertical size of the CU before partitioning, or may respectively havesizes smaller than a horizontal size and a vertical size beforepartitioning according to a number of times of partitioning. The CU maybe recursively partitioned into a plurality of CUs. By the recursivepartitioning, at least one among a height and a width of a CU afterpartitioning may decrease comparing with at least one among a height anda width of a CU before partitioning. Partitioning of the CU may berecursively performed until to a predefined depth or predefined size.For example, a depth of a CTU may be 0, and a depth of a smallest codingunit (SCU) may be a predefined maximum depth. Herein, the CTU may be acoding unit having a maximum coding unit size, and the SCU may be acoding unit having a minimum coding unit size as described above.Partitioning is started from the CTU 310, a CU depth increases by 1 as ahorizontal size or a vertical size or both of the CU decreases bypartitioning. For example, for each depth, a CU which is not partitionedmay have a size of 2N×2N. Also, in case of a CU which is partitioned, aCU with a size of 2N×2N may be partitioned into four CUs with a size ofN×N. A size of N may decrease to half as a depth increase by 1.

In addition, information whether or not the CU is partitioned may berepresented by using partition information of the CU. The partitioninformation may be 1-bit information. All CUs, except for a SCU, mayinclude partition information. For example, when a value of partitioninformation is the first value, the CU may not be partitioned, when avalue of partition information is the second value, the CU may bepartitioned.

Referring to FIG. 3, a CTU having a depth 0 may be a 64×64 block. 0 maybe a minimum depth. A SCU having a depth 3 may be an 8×8 block. 3 may bea maximum depth. A CU of a 32×32 block and a 16×16 block may berespectively represented as a depth 1 and a depth 2.

For example, when a single coding unit is partitioned into four codingunits, a horizontal size and a vertical size of the four partitionedcoding units may be a half size of a horizontal and vertical size of theCU before being partitioned. In one embodiment, when a coding unithaving a 32×32 size is partitioned into four coding units, each of thefour partitioned coding units may have a 16×16 size. When a singlecoding unit is partitioned into four coding units, it may be called thatthe coding unit may be partitioned (quad-tree partitioned) into aquad-tree form.

For example, when a single coding unit is partitioned into two codingunits, a horizontal or vertical size of the two coding units may be ahalf of a horizontal or vertical size of the coding unit before beingpartitioned. For example, when a coding unit having a 32×32 size ispartitioned in a vertical direction, each of two partitioned codingunits may have a size of 16×32. For example, when a coding unit having asize of 8×32 is horizontally partitioned into two sub-coding units, eachof the two sub-coding units may have a size of 8×16. When a singlecoding unit is partitioned into two coding units, it may be called thatthe coding unit is partitioned (binary-tree partitioned) in abinary-tree form.

For example, when one coding unit is partitioned into three sub-codingunits, the horizontal or vertical size of the coding unit can bepartitioned with a ratio of 1:2:1, thereby producing three sub-codingunits whose horizontal or vertical sizes are in a ratio of 1:2:1. Forexample, when a coding unit having a size of 16×32 is horizontallypartitioned into three sub-coding units, the three sub-coding units mayhave sizes of 16×8, 16×16, and 16×8 respectively, in the order from theuppermost to the lowermost sub-coding unit. For example, when a codingunit having a size of 32×32 is vertically split into three sub-codingunits, the three sub-coding units may have sizes of 8×32, 16×32, and8×32, respectively in the order from the left to the right sub-codingunit. When one coding unit is partitioned into three sub-coding units,it can be said that the coding unit is ternary-tree partitioned orpartitioned by a ternary tree partition structure.

In FIG. 3, a coding tree unit (CTU) 320 is an example of a CTU to whicha quad tree partition structure, a binary tree partition structure, anda ternary tree partition structure are all applied.

As described above, in order to partition the CTU, at least one of aquad tree partition structure, a binary tree partition structure, and aternary tree partition structure may be applied. Various tree partitionstructures may be sequentially applied to the CTU, according to apredetermined priority order. For example, the quad tree partitionstructure may be preferentially applied to the CTU. A coding unit thatcannot be partitioned any longer using a quad tree partition structuremay correspond to a leaf node of a quad tree. A coding unitcorresponding to a leaf node of a quad tree may serve as a root node ofa binary and/or ternary tree partition structure. That is, a coding unitcorresponding to a leaf node of a quad tree may be further partitionedby a binary tree partition structure or a ternary tree partitionstructure, or may not be further partitioned. Therefore, by preventing acoding block that results from binary tree partitioning or ternary treepartitioning of a coding unit corresponding to a leaf node of a quadtree from undergoing further quad tree partitioning, block partitioningand/or signaling of partition information can be effectively performed.

The fact that a coding unit corresponding to a node of a quad tree ispartitioned may be signaled using quad partition information. The quadpartition information having a first value (e.g., “1”) may indicate thata current coding unit is partitioned by the quad tree partitionstructure. The quad partition information having a second value (e.g.,“0”) may indicate that a current coding unit is not partitioned by thequad tree partition structure. The quad partition information may be aflag having a predetermined length (e.g., one bit).

There may not be a priority between the binary tree partitioning and theternary tree partitioning. That is, a coding unit corresponding to aleaf node of a quad tree may further undergo arbitrary partitioningamong the binary tree partitioning and the ternary tree partitioning. Inaddition, a coding unit generated through the binary tree partitioningor the ternary tree partitioning may undergo a further binary treepartitioning or a further ternary tree partitioning, or may not befurther partitioned.

A tree structure in which there is no priority among the binary treepartitioning and the ternary tree partitioning is referred to as amulti-type tree structure. A coding unit corresponding to a leaf node ofa quad tree may serve as a root node of a multi-type tree. Whether topartition a coding unit which corresponds to a node of a multi-type treemay be signaled using at least one of multi-type tree partitionindication information, partition direction information, and partitiontree information. For partitioning of a coding unit corresponding to anode of a multi-type tree, the multi-type tree partition indicationinformation, the partition direction, and the partition tree informationmay be sequentially signaled.

The multi-type tree partition indication information having a firstvalue (e.g., “1”) may indicate that a current coding unit is to undergoa multi-type tree partitioning. The multi-type tree partition indicationinformation having a second value (e.g., “0”) may indicate that acurrent coding unit is not to undergo a multi-type tree partitioning.

When a coding unit corresponding to a node of a multi-type tree ispartitioned by a multi-type tree partition structure, the coding unitmay further include partition direction information. The partitiondirection information may indicate in which direction a current codingunit is to be partitioned for the multi-type tree partitioning. Thepartition direction information having a first value (e.g., “1”) mayindicate that a current coding unit is to be vertically partitioned. Thepartition direction information having a second value (e.g., “0”) mayindicate that a current coding unit is to be horizontally partitioned.

When a coding unit corresponding to a node of a multi-type tree ispartitioned by a multi-type tree partition structure, the current codingunit may further include partition tree information. The partition treeinformation may indicate a tree partition structure which is to be usedfor partitioning of a node of a multi-type tree. The partition treeinformation having a first value (e.g., “1”) may indicate that a currentcoding unit is to be partitioned by a binary tree partition structure.The partition tree information having a second value (e.g., “0”) mayindicate that a current coding unit is to be partitioned by a ternarytree partition structure.

The partition indication information, the partition tree information,and the partition direction information may each be a flag having apredetermined length (e.g., one bit).

At least any one of the quad-tree partition indication information, themulti-type tree partition indication information, the partitiondirection information, and the partition tree information may be entropyencoded/decoded. For the entropy-encoding/decoding of those types ofinformation, information on a neighboring coding unit adjacent to thecurrent coding unit may be used. For example, there is a highprobability that the partition type (the partitioned or non-partitioned,the partition tree, and/or the partition direction) of a leftneighboring coding unit and/or an upper neighboring coding unit of acurrent coding unit is similar to that of the current coding unit.Therefore, context information for entropy encoding/decoding of theinformation on the current coding unit may be derived from theinformation on the neighboring coding units. The information on theneighboring coding units may include at least any one of quad partitioninformation, multi-type tree partition indication information, partitiondirection information, and partition tree information.

As another example, among binary tree partitioning and ternary treepartitioning, binary tree partitioning may be preferentially performed.That is, a current coding unit may primarily undergo binary treepartitioning, and then a coding unit corresponding to a leaf node of abinary tree may be set as a root node for ternary tree partitioning. Inthis case, neither quad tree partitioning nor binary tree partitioningmay not be performed on the coding unit corresponding to a node of aternary tree.

A coding unit that cannot be partitioned by a quad tree partitionstructure, a binary tree partition structure, and/or a ternary treepartition structure becomes a basic unit for coding, prediction and/ortransformation. That is, the coding unit cannot be further partitionedfor prediction and/or transformation. Therefore, the partition structureinformation and the partition information used for partitioning a codingunit into prediction units and/or transformation units may not bepresent in a bitstream.

However, when the size of a coding unit (i.e., a basic unit forpartitioning) is larger than the size of a maximum transformation block,the coding unit may be recursively partitioned until the size of thecoding unit is reduced to be equal to or smaller than the size of themaximum transformation block. For example, when the size of a codingunit is 64×64 and when the size of a maximum transformation block is32×32, the coding unit may be partitioned into four 32×32 blocks fortransformation. For example, when the size of a coding unit is 32×64 andthe size of a maximum transformation block is 32×32, the coding unit maybe partitioned into two 32×32 blocks for the transformation. In thiscase, the partitioning of the coding unit for transformation is notsignaled separately, and may be determined through comparison betweenthe horizontal or vertical size of the coding unit and the horizontal orvertical size of the maximum transformation block. For example, when thehorizontal size (width) of the coding unit is larger than the horizontalsize (width) of the maximum transformation block, the coding unit may bevertically bisected. For example, when the vertical size (height) of thecoding unit is larger than the vertical size (height) of the maximumtransformation block, the coding unit may be horizontally bisected.

Information of the maximum and/or minimum size of the coding unit andinformation of the maximum and/or minimum size of the transformationblock may be signaled or determined at an upper level of the codingunit. The upper level may be, for example, a sequence level, a picturelevel, a slice level, or the like. For example, the minimum size of thecoding unit may be determined to be 4×4. For example, the maximum sizeof the transformation block may be determined to be 64×64. For example,the minimum size of the transformation block may be determined to be4×4.

Information of the minimum size (quad tree minimum size) of a codingunit corresponding to a leaf node of a quad tree and/or information ofthe maximum depth (the maximum tree depth of a multi-type tree) from aroot node to a leaf node of the multi-type tree may be signaled ordetermined at an upper level of the coding unit. For example, the upperlevel may be a sequence level, a picture level, a slice level, or thelike. Information of the minimum size of a quad tree and/or informationof the maximum depth of a multi-type tree may be signaled or determinedfor each of an intra slice and an inter slice.

Difference information between the size of a CTU and the maximum size ofa transformation block may be signaled or determined at an upper levelof the coding unit. For example, the upper level may be a sequencelevel, a picture level, a slice level, or the like. Information of themaximum size of the coding units corresponding to the respective nodesof a binary tree (hereinafter, referred to as a maximum size of a binarytree) may be determined based on the size of the coding tree unit andthe difference information. The maximum size of the coding unitscorresponding to the respective nodes of a ternary tree (hereinafter,referred to as a maximum size of a ternary tree) may vary depending onthe type of slice. For example, for an intra slice, the maximum size ofa ternary tree may be 32×32. For example, for an inter slice, themaximum size of a ternary tree may be 128×128. For example, the minimumsize of the coding units corresponding to the respective nodes of abinary tree (hereinafter, referred to as a minimum size of a binarytree) and/or the minimum size of the coding units corresponding to therespective nodes of a ternary tree (hereinafter, referred to as aminimum size of a ternary tree) may be set as the minimum size of acoding block.

As another example, the maximum size of a binary tree and/or the maximumsize of a ternary tree may be signaled or determined at the slice level.Alternatively, the minimum size of the binary tree and/or the minimumsize of the ternary tree may be signaled or determined at the slicelevel.

Depending on size and depth information of the above-described variousblocks, quad partition information, multi-type tree partition indicationinformation, partition tree information and/or partition directioninformation may be included or may not be included in a bit stream.

For example, when the size of the coding unit is not larger than theminimum size of a quad tree, the coding unit does not contain quadpartition information. Thus, the quad partition information may bededuced from a second value.

For example, when the sizes (horizontal and vertical sizes) of a codingunit corresponding to a node of a multi-type tree are larger than themaximum sizes (horizontal and vertical sizes) of a binary tree and/orthe maximum sizes (horizontal and vertical sizes) of a ternary tree, thecoding unit may not be binary-tree partitioned or ternary-treepartitioned. Accordingly, the multi-type tree partition indicationinformation may not be signaled but may be deduced from a second value.

Alternatively, when the sizes (horizontal and vertical sizes) of acoding unit corresponding to a node of a multi-type tree are the same asthe maximum sizes (horizontal and vertical sizes) of a binary treeand/or are two times as large as the maximum sizes (horizontal andvertical sizes) of a ternary tree, the coding unit may not be furtherbinary-tree partitioned or ternary-tree partitioned. Accordingly, themulti-type tree partition indication information may not be signaled butbe derived from a second value. This is because when a coding unit ispartitioned by a binary tree partition structure and/or a ternary treepartition structure, a coding unit smaller than the minimum size of abinary tree and/or the minimum size of a ternary tree is generated.

Alternatively, when the depth of a coding unit corresponding to a nodeof a multi-type tree is equal to the maximum depth of the multi-typetree, the coding unit may not be further binary-tree partitioned and/orternary-tree partitioned. Accordingly, the multi-type tree partitionindication information may not be signaled but may be deduced from asecond value.

Alternatively, only when at least one of vertical direction binary treepartitioning, horizontal direction binary tree partitioning, verticaldirection ternary tree partitioning, and horizontal direction ternarytree partitioning is possible for a coding unit corresponding to a nodeof a multi-type tree, the multi-type tree partition indicationinformation may be signaled. Otherwise, the coding unit may not bebinary-tree partitioned and/or ternary-tree partitioned. Accordingly,the multi-type tree partition indication information may not be signaledbut may be deduced from a second value.

Alternatively, only when both of the vertical direction binary treepartitioning and the horizontal direction binary tree partitioning orboth of the vertical direction ternary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingunit corresponding to a node of a multi-type tree, the partitiondirection information may be signaled. Otherwise, the partitiondirection information may not be signaled but may be derived from avalue indicating possible partitioning directions.

Alternatively, only when both of the vertical direction binary treepartitioning and the vertical direction ternary tree partitioning orboth of the horizontal direction binary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingtree corresponding to a node of a multi-type tree, the partition treeinformation may be signaled. Otherwise, the partition tree informationmay not be signaled but be deduced from a value indicating a possiblepartitioning tree structure.

FIG. 4 is a view showing an intra-prediction process.

Arrows from center to outside in FIG. 4 may represent predictiondirections of intra prediction modes.

Intra encoding and/or decoding may be performed by using a referencesample of a neighbor block of the current block. A neighbor block may bea reconstructed neighbor block. For example, intra encoding and/ordecoding may be performed by using an encoding parameter or a value of areference sample included in a reconstructed neighbor block.

A prediction block may mean a block generated by performing intraprediction. A prediction block may correspond to at least one among CU,PU and TU. A unit of a prediction block may have a size of one among CU,PU and TU. A prediction block may be a square block having a size of2×2, 4×4, 16×16, 32×32 or 64×64 etc. or may be a rectangular blockhaving a size of 2×8, 4×8, 2×16, 4×16 and 8×16 etc.

Intra prediction may be performed according to intra prediction mode forthe current block. The number of intra prediction modes which thecurrent block may have may be a fixed value and may be a valuedetermined differently according to an attribute of a prediction block.For example, an attribute of a prediction block may comprise a size of aprediction block and a shape of a prediction block, etc.

The number of intra-prediction modes may be fixed to N regardless of ablock size. Or, the number of intra prediction modes may be 3, 5, 9, 17,34, 35, 36, 65, or 67 etc. Alternatively, the number of intra-predictionmodes may vary according to a block size or a color component type orboth. For example, the number of intra prediction modes may varyaccording to whether the color component is a luma signal or a chromasignal. For example, as a block size becomes large, a number ofintra-prediction modes may increase. Alternatively, a number ofintra-prediction modes of a luma component block may be larger than anumber of intra-prediction modes of a chroma component block.

An intra-prediction mode may be a non-angular mode or an angular mode.The non-angular mode may be a DC mode or a planar mode, and the angularmode may be a prediction mode having a specific direction or angle. Theintra-prediction mode may be expressed by at least one of a mode number,a mode value, a mode numeral, a mode angle, and mode direction. A numberof intra-prediction modes may be M, which is equal to or larger than 1,including the non-angular and the angular mode.

In order to intra-predict a current block, a step of determining whetheror not samples included in a reconstructed neighbor block may be used asreference samples of the current block may be performed. When a samplethat is not usable as a reference sample of the current block ispresent, a value obtained by duplicating or performing interpolation onat least one sample value among samples included in the reconstructedneighbor block or both may be used to replace with a non-usable samplevalue of a sample, thus the replaced sample value is used as a referencesample of the current block.

When intra-predicting, a filter may be applied to at least one of areference sample and a prediction sample based on an intra-predictionmode and a current block size/shape.

In case of a planar mode, when generating a prediction block of acurrent block, according to a position of a prediction target samplewithin a prediction block, a sample value of the prediction targetsample may be generated by using a weighted sum of an upper and leftside reference sample of a current sample, and a right upper side andleft lower side reference sample of the current block. In addition, incase of a DC mode, when generating a prediction block of a currentblock, an average value of upper side and left side reference samples ofthe current block may be used. In addition, in case of an angular mode,a prediction block may be generated by using an upper side, a left side,a right upper side, and/or a left lower side reference sample of thecurrent block. In order to generate a prediction sample value,interpolation of a real number unit may be performed.

An intra-prediction mode of a current block may be entropyencoded/decoded by predicting an intra-prediction mode of a blockpresent adjacent to the current block. When intra-prediction modes ofthe current block and the neighbor block are identical, information thatthe intra-prediction modes of the current block and the neighbor blockare identical may be signaled by using predetermined flag information.In addition, indicator information of an intra-prediction mode that isidentical to the intra-prediction mode of the current block amongintra-prediction modes of a plurality of neighbor blocks may besignaled. When intra-prediction modes of the current block and theneighbor block are different, intra-prediction mode information of thecurrent block may be entropy encoded/decoded by performing entropyencoding/decoding based on the intra-prediction mode of the neighborblock.

FIG. 5 is a view showing intra-prediction according to the presentinvention.

Intra-prediction of a current block may include: step S510 of derivingan intra-prediction mode, step S520 of configuring a reference sample,and/or step S530 of performing intra-prediction.

In step S510, an intra-prediction mode of a current block may bederived. The intra-prediction mode of the current block may be derivedby using a method of using an intra-prediction mode of a neighbor block,a method of entropy encoding/decoding an intra-prediction mode of acurrent block from a bitstream, a method of using a coding parameter ofa neighbor block or a method of using intra prediction mode of a colorcomponent. According to the method of using the intra-prediction mode ofthe neighbor block, the intra-prediction mode of the current block maybe derived by using at least one of an intra-prediction mode derived byusing an intra-prediction mode of a neighbor block, a combination of atleast one intra-prediction mode of a neighbor block, and at least oneMPM.

In step S520, a reference sample may be configured by performing atleast one of reference sample selecting, reference sample padding andreference sample filtering.

In step S530, intra-prediction may be performed by performing at leastone of non-angular prediction, angular prediction, positionalinformation based prediction, inter color component prediction, andrepresentative sample-based intra-prediction. When representativesample-based intra-prediction is performed, intra-prediction may beperformed based on at least one representative sample inside a block.Representative sample-based prediction may perform at least one amongdividing a block, determining a representative sample,predicting/transforming/quantizing a representative sample andrepresentative sample-based intra-prediction. In step S530, filtering ona prediction sample may be additionally performed.

In order to derive the intra-prediction mode of the current block, atleast one reconstructed neighbor block may be used. A position of thereconstructed neighbor block may be a fixed position that is predefined,or may be a position derived by encoding/decoding. Hereinafter,encoding/decoding may mean entropy encoding and decoding. For example,when a coordinate of a left upper corner side sample of a current blockhaving a W×H size is (0, 0), a neighbor block may be at least one ofblocks adjacent to coordinate of (−1, H−1), (W−1, −1), (W, −1), (−1, H),and (−1, −1), and neighbor blocks of the above blocks. Here, W and H mayrepresent length or the number of samples of width (W) and height (H) ofthe current block.

An intra-prediction mode of a neighbor block which is not available maybe replaced with a predetermined intra-prediction mode. Thepredetermined intra-prediction mode may be, for example, a DC mode, aplanar mode, a vertical mode, a horizontal mode, and/or a diagonal mode.For example, when a neighbor block is positioned outside of a boundaryof at least one predetermined unit of a picture, a slice, a tile, and acoding tree unit, the neighbor block is inter-predicted, or when theneighbor block is encoded in a PCM mode, the corresponding block may bedetermined as non-available. Alternatively, when the neighbor block isunavailable, the intra prediction mode of the corresponding block is notreplaced and not used.

The intra-prediction mode of the current block may be derived as astatistical value of an intra-prediction mode of a predeterminedpositional neighbor block or an intra-prediction mode of at least twoneighbor blocks. In the present description, the statistical value maymean at least one of an average value, a maximum value, a minimum value,a mode, a median value, a weighted average value, and an interpolationvalue.

Alternatively, the intra-prediction mode of the current block may bederived based on a size of neighbor blocks. For example, anintra-prediction mode of a neighbor block having relatively large sizemay be derived as the intra-prediction mode of the current block.Alternatively, a statistical value may be calculated by assigning alarge weight on an intra-prediction mode of a block having relativelylarge size. Alternatively, a mode to which a relatively large weight isassigned may be pre-defined or signaled. For example, a relatively largeweight may be assigned to at least one among a vertical directionalmode, a horizontal directional mode, a diagonal directional mode andnon-directional mode. The same weight may be assigned to the abovemodes.

Alternatively, whether or not the intra-prediction mode of the neighborblock is angular mode may be considered. For example, when theintra-prediction mode of the neighbor block is a non-angular mode, thenon-angular mode may be derived as the intra-prediction mode of thecurrent block. Alternatively, an intra-prediction mode of other neighborblock, except for the non-angular mode, may be derived as theintra-prediction mode of the current block.

In order to derive the intra-prediction mode of the current block, oneor more most probable mode (MPM) lists may be configured by using anintra-prediction mode of a neighbor block. A number N of candidate modesincluded in an MPM list may be fixed, or may be determined according toa size or form or both of the current block. The MPM list may beconfigured not to include an overlapped mode. When a number of availablecandidate modes is smaller than N, a predetermined candidate mode amongavailable candidate modes, for example, a mode obtained by adding orsubtracting a predetermined offset to an angular mode may be added tothe one or more MPM lists. Alternatively, at least one of a horizontalmode, a vertical mode, a 45 angular mode, a 135 angular mode, a 225angular mode, and a non-angular mode may be added to the MPM list. Thepredetermined offset may be 1, 2, 3, 4, or a positive integer. An MPMflag indicating whether a mode that matches the intra prediction mode ofthe current block is present within the MPM list may be signaled. Whenthe MPM flag has a value of 1, MPM index information mpm_idx indicatingthe matched mode within the MPM list may be signaled. On the other hand,when the MPM flag has a value of 0, remaining mode informationrem_intra_luma_pred_mode for informing of the intra prediction mode ofthe current block may be signaled. Either one or both of the MPM indexinformation and the remaining mode information may not be signaled whena multiple reference sample line-based prediction is performed or when aweighted sum operation of calculating the weighted sum of an intraprediction value and an inter prediction value is performed. Forexample, when multiple sample lines are used (i.e., mrl_index is a valueother than 0), the MPM flag or the remaining mode information may not besignaled. For example, when the weighted sum operation of the intraprediction value and the inter prediction value is performed, theremaining mode information may not be signaled.

The MPM list may be configured in a predetermined sequence based on aposition of the neighbor block. For example, the predetermined sequencemay be a sequence of blocks adjacent to a left side, an upper side, aleft lower corner side, a right upper corner side, and a left uppercorner side of the current block. A non-angular mode may be included inthe MPM list at an arbitrary position. For example, it may be added nextto intra-prediction modes of blocks adjacent to a left side and an upperside.

An MPM list generated based on the current block may be used as an MPMlist for at least one sub block included in the current block. An orderbetween candidate modes configuring an MPM list, the number of candidatemodes included in an MPM list, etc, may be determined based on a size, aform and/or a component of the current block.

Alternatively, a group of modes may be configured by selecting a part ofmodes among modes which are not included in an MPM list. The configuredgroup of modes may be utilized as another list. For example, a group ofmodes may be configured using modes which are obtained by sampling witha predetermined interval after arranging modes which are not MPMcandidates, or using modes which are obtained by adding/subtracting n (nis an integer equal to or larger than 1) to/from a MPM candidate mode.

When constructing the MPM list, the MPM list can be differentlyconstructed depending on at least one element selected from among theslice type, the encoding mode, and the multiple reference sample lines.That is, the MPM list can be constructed while changing at least oneelement selected from among the number of MPMs, the order in which MPMsare derived, the MPM candidate modes, and the default mode. For example,an MPM list for an I-slice and an MPM list for a P or B slice aredifferently constructed. For example, an MPM list for an I slice isconstructed by deriving six MPM candidate modes, and an MPM list for a Por B slice is constructed by deriving three MPM candidate modes. Forexample, an MPM list for a case where the encoding mode of the currentblock is an intra mode and an MPM list for a case where the encodingmode of the current block is an inter mode are constructed in differentmanners. The inter modes may include a mode in which prediction isperformed using the waited sum of an inter prediction value and an intraprediction value. The intra prediction mode for performing an intraprediction, performed in the process of performing prediction using theinter mode, may be derived, and the derived mode may be used toconstruct the MPM list. In this case, MPM candidate modes are limited toa small number of candidate modes. The MPM candidate modes include, forexample, at least one of DC mode, Planar mode, horizontal mode, andvertical mode. For example, in the case where multiple reference samplelines are utilized (i.e., mrl_index has a value other than 0), the MPMlist may be differently constructed. That is, the MPM candidate modesinclude intra prediction modes allowing the multiple reference sampleline-based prediction. When non-directional modes, such as DC mode andPlanar mode, do not allow the multiple reference sample line-basedprediction, the non-directional modes are not considered as the MPMcandidate. In other words, the MPM list may be constructed by using onlyone or more directional modes.

According to a further embodiment of the present invention relating to amethod of deriving an intra prediction mode, an intra prediction mode ofa current block may be derived by using an intra prediction mode of adifferent color component. For example, when the current block is achroma block, an intra prediction mode of a luma block corresponding tothe chroma block can be used to derive an intra prediction mode of thechroma block. As the luma block corresponding to the chroma block, theremay be one or more luma blocks. The corresponding luma block may bedetermined depending on at least any one of the size, the shape, and theencoding parameter of a chroma block. Alternatively, the correspondingluma block may be determined depending on at least any one of the size,the shape, and the encoding parameter of a luma block.

The luma block corresponding to the chroma block may be composed of aplurality of partitions. All or part of the plurality of partitions mayhave different intra prediction modes thereof. An intra prediction modeof the chroma block may be derived on the basis of all or part of theplurality of partitions included in the corresponding luma block. Inthis case, some partitions may be selectively used, in which the usedpartitions are selected based on the comparison of the block size, theshape, the depth information, etc. of the chroma block with those of theluma block (all or part of the plurality of partitions). A partition ata position in the luma block corresponding to a predetermined positionin the chroma block may be selectively used. The predetermined positionmay refer to a corner sample (e.g., upper left sample) position in thechroma block or a center sample position in the chroma block.

The method of deriving an intra prediction mode of one color componentblock using an intra prediction mode of a different color componentblock (i.e. inter color component intra prediction mode) according tothe present invention is not limited to the example in which an intraprediction mode of a luma block corresponding to a chroma block is used.For example, an intra prediction mode of a chroma block may be derivedby using or sharing at least any one of an MPM index mpm_idx and an MPMlist of a luma block corresponding to the chroma block.

FIG. 6 is an exemplary diagram illustrating the relationship between aluma block and a chroma block.

In the example illustrated in FIG. 6, a sample ratio of color componentsis 4:2:0, and at least one of luma blocks A, B, C, and D corresponds toone chroma block.

With reference to FIG. 6, an intra prediction mode of one chroma blockmay be derived by using an intra prediction mode of the luma block Acorresponding to a sample at an upper left position (0,0) in the chromablock or an intra prediction mode of the luma block D corresponding to asample at a center position (ns/2, ns/2) in the chroma block. Thepredetermined position in the chroma block is not limited to the upperleft position (0, 0) or the center position (nS/2, nS/2). For example,The predetermined position may be an upper right position, a lower leftposition, and/or a lower right position. A center position of the chromablock may be (W/2, H/2) where W is block width and H is block height.

The predetermined position may be selected on the basis of the shape ofthe chroma block. For example, with the chroma block having a squareshape, the predetermined position may be a center sample position. Withthe chroma block having an oblong shape, the predetermined position maybe an upper left sample position. Alternatively, the predeterminedposition may be a position of an upper left sample in the chroma blockhaving a square shape or a position of a center sample in the chromablock having an oblong shape.

According to a further embodiment, an intra prediction mode of a chromablock may be derived by using statistic figures of one or more intraprediction modes of a luma block having an equal size to the chromablock.

In the example illustrated in FIG. 6, a mode corresponding to theaverage of the intra prediction modes of the luma blocks A and D or amode corresponding to the average of the intra prediction modes ofblocks A, B, C, and D inside the luma block corresponding to the size ofthe chroma block is derived as the intra prediction mode of the chromablock.

When there are multiple intra prediction modes of available luma blocks,all or part of them may be selected. The selection is performed based onthe predetermined position in the chroma block or based on the size(s),the shape(s), and/or the depth(s) of the chroma block, the luma block,or both. The intra prediction mode of the chroma block can be derived byusing the selected intra prediction mode of the luma block.

For example, the size of the luma block A corresponding to the upperleft sample position (0,0) in the chroma block and the size of theluminance bock D corresponding to the center sample position (nS/2,nS/2) in the chroma block are compared, and the intra prediction mode ofthe luma block D having a larger size may be used to derive the intraprediction mode of the chroma block.

Alternatively, when the size of a luma block corresponding to apredetermined position in a chroma block is equal to or larger than thesize of the chroma block, an intra prediction mode of the chroma blockis derived by using the intra prediction module of the luma block.

Alternatively, when the size of a chroma block is within a predeterminedrange, an intra prediction mode of the chroma block is derived by usingan intra prediction mode of a luma block corresponding to the upper leftsample position (0, 0) in the chroma block.

Alternatively, when the size of a chroma block is within a predeterminedrange, the size of a luma block corresponding to a predeterminedposition (0, 0) of the chroma block and the size of a luma blockdisposed at another predetermined position (nS/2, nS/2) of the chromablock are compared, and an intra prediction mode of the chroma block isderived by using the intra prediction mode of the luma block having alarger size.

The predetermined range may be derived from at least any one piece ofinformation among information signaled through a bitstream, informationof the size (and/or depth) of a block (a chroma block, a luma block, orboth), and information predefined in an encoder or a decoder.

Alternatively, when a chroma block has an oblong shape, an intraprediction mode of the chroma block may be derived by using an intraprediction mode of a luma block corresponding to a center sampleposition (ns/2, ns2) in the chroma block.

Among the plurality of partitions of the luma block, a partition havingthe same shape as the chroma block may be used. For example, when thechroma block has a square shape or a non-square shape, a partitionhaving a square shape or a non-square shape, selected among theplurality of partitions of the luma block, may be used.

In the example described with reference to FIG. 6, the method ofderiving an intra prediction mode of a chroma block using an intraprediction mode of a luma block also applies to a case in which an intraprediction mode of a luma block is used as an intra prediction mode of achroma block as it is. The method of deriving an intra prediction modeof a chroma block is not limited to the method of using an intraprediction mode of the corresponding luma block. For example, an intraprediction mode of a chroma block can be derived from information,including an MPM list and an MPM index mpm_idx, which is used to derivean intra prediction mode of a luma block.

Alternatively, the MPM list of the chroma block can be constructed usingthe intra prediction mode of the luma block corresponding to the sampleof the predetermined position in the chroma block. In this case, thempm-idx information of the chroma block may be encoded and signaled. TheMPM list of the chroma block may be constructed in a similar way to theconstruction of the MPM list of the luma block. MPM candidates of thechroma block may include intra prediction modes of neighbor chromablocks and/or intra prediction modes of luma blocks corresponding to thechroma block.

When an MPM flag is 0, a second MPM list including at least oneintra-prediction mode may be configured, and the intra-prediction modeof the current block may be derived by using a second MPM index(2nd_mpm_idx). Herein, a second indicator (for example, a second MPMflag) indicating whether or not the intra-prediction mode of the currentblock is included in the second MPM list may be encoded/decoded. Similarto a first MPM list, the second MPM list may be configured by usingintra-prediction modes of the neighbor block. Herein, theintra-prediction mode included in the first MPM list may not be includedin the second MPM list. A number of MPM lists is not limited to 1 or 2,N MPM lists may be used.

When the intra-prediction mode of the current block is not included inone of a plurality of MPM lists, a luma component intra-prediction modeof the current block may be encoded/decoded. In addition, a chromacomponent intra-prediction mode may be derived and encoded/decoded basedon an associated luma component intra-prediction mode.

When the current block is partitioned into a plurality of sub-blocks, inorder to derive an intra-prediction mode of each sub-block, at least oneof the described methods may be applied.

A size or form or both of a sub-block may be a predetermined size orform or both (for example, 4×4), or may be determined according to asize or form or both of the current block. Alternatively, the size ofthe sub-block may be determined based on whether or not a neighbor blockof the current block is partitioned, or may be determined based on anintra-prediction mode of a neighbor block of the current block. Forexample, the current block may be partitioned based on a boundary atwhich an intra-prediction mode of a neighbor block is different.Alternatively, the current block may be partitioned based on whether theneighbor block is an intra coding block or an inter coding block.

An indicator (for example, NDIP_flag) representing that theintra-prediction mode of the current block is derived by using theintra-prediction mode of the neighbor block may be encoded/decoded. Theindicator may be encoded/decoded by at least one unit of the currentblock and the sub-block. Herein, when a size of the current block or thesub-block corresponds to a predetermined size or a predetermined sizerange, the indicator may be encoded/decoded.

Determining whether or not the size of the current block corresponds toa predetermined size may be performed based on a horizontal or verticallength of the current block. For example, when the horizontal orvertical length is a length capable of being partitioned, it isdetermined that the size of the current block corresponds to apredetermined size.

Intra-prediction information may be signaled through at least one of avideo parameter set (VPS), a sequence parameter set (SPS), a pictureparameter set (PPS), an adaptation parameter set (APS), a slice header,and a tile header. In a predetermined block size or less, at least onepiece of intra-prediction information may not be signaled. Herein,intra-prediction information of a previously encoded/decoded block (forexample, higher block) may be used.

A reference sample for intra-prediction may be configured based on thederived intra-prediction mode. In the description hereinafter, a currentblock may mean a prediction block or a sub-block having a size/formsmaller than a size/form of the prediction block. The reference samplemay be configured by using at least one sample reconstructed adjacent toa current block or by using a combination of samples. In addition,filtering may be applied to the configured reference sample.

A number or position or both of reconstructed sample lines used forconfiguring the reference sample may vary according to a position of acurrent block within a coding tree block. Each reconstructed sample on aplurality of reconstructed sample lines may be used as a referencesample at it is. Alternatively, a predetermined filter may be applied tothe reconstructed sample, and a reference sample may be generated byusing the filtered reconstructed sample. Reconstructed samples to whicha filter is applied may be included in the same reconstructed sampleline or in different reconstructed sample lines.

An indicator indicating whether multiple reference sample lines areutilized for prediction may be signaled. For example, an indicator suchas mrl_enabled_flag may be included in at least one of an SPS, a PPS,and a slice header so as to be signaled. The flag may be an indicatorindicating whether a single reference sample line is used or multiplereference sample lines are used.

When the indicator indicates that multiple reference sample lines areused, reference sample line indexes are also signaled. For example,mrl_index is signaled. Therefore, it is possible to determine whichreference sample lines are used.

When the indicator mrl_index has a value of 0, a first reference sampleline which is closest to the current block is utilized. On the otherhand, when the indicator mrl_index has a value of 1, a second referencesample line which is second closest to the current block is utilized.When the indicator mrl_index has a value of 2, a third reference sampleline which is third closest to the current block is used. The first tofourth reference sample lines respectively correspond to reconstructedsample lines 1 to 4 illustrated in FIG. 7, respectively.

The indicator mrl_index is signaled depending on at least one of theintra prediction mode, the MPM information, the size (with and height)of the current block, the presence or absence of an upper boundary of aCTU, and the color component. When the indicator mrl_index is notsignaled, the first reference sample line adjacent to the current blockis used.

For example, when the intra prediction mode is a predetermined mode, theindicator mrl_index may be signaled. The intra prediction mode may bethe intra prediction mode of the current block or at least one of theintra prediction modes of the respective neighboring blocks. Thepredetermined mode is at least one of non-directional prediction mode,directional prediction mode, vertical or horizontal mode, even-numberedmode, and odd-numbered mode. For example, when the intra prediction modeof a neighboring block adjacent to the left boundary or the upperboundary of the current block is one of directional modes, the indicatormrl_index may be signaled. Alternatively, when the intra prediction modeof the neighboring block is one of even-numbered modes or one ofodd-numbered modes, the indicator mrl_index may be signaled.

For example, the indicator mrl_index may be signaled on the basis of theMPM information of the current block. The MPM information include atleast one of an MPM flag, an MPM index, an MPM list, and an MPMcandidate. For example, when the MPM flag for the intra prediction modeof the current block indicates matching, the indicator mrl_index may besignaled. Alternatively, when any one directional prediction mode ispresent within an MPN candidate list or only directional predictionmodes are present within the MPN candidate list, the indicator mrl_indexmay be signaled. Alternatively, when any one non-directional predictionmode is present in the MPM candidate line, the indicator mrl_index maybe signaled. Alternatively, the MPM information of the current block issignaled differently depending on the indicator mrl_index. For example,when the indicator mrl_index has a value other than 0, at least onepiece of the MPM information may not be signaled. For example, when theindicator mrl_index has a value other than 0, the MPM flag or theremaining mode information may not be signaled. On the other hand, whenthe indicator mrl_index has a value other than 0, the MPM index may besignaled and the intra prediction mode of the current block may bederived using the MPM index. For example, when the indicator mrl_indexhas a value other than 0, the MPM mode may be determined without parsingthe MPM flag.

For example, when the size (width or height) of the current block iswithin a predetermined size range, the indicator mrl_index may besignaled. For example, when the size (width or height) is larger than apredetermined size (e.g., 4), the indicator mrl_index may be signaled.

For example, the indicator mrl_index may be signaled depending onwhether the current block is located at the upper boundary of a CTU. Forexample, when the current block is located at the upper boundary of aCTU, the indicator mrl_index may not be signaled.

For example, the indictor mrl_index may be signaled when the colorcomponent of the current block is a luminance signal, and the indicatormrl_index indicator may not be signaled when the color component is achrominance signal.

Alternatively, the indicator mrl_index refers to a reference sample lineto be used optionally. For example, the first reference sample lineadjacent to the current block may be always used, and the referencesample line indicated by the indicator mrl_index indicator may beoptionally used.

When multiple reference sample lines are used, whether to applyfiltering is determined for each reference sample line. For example, onthe basis of the intra prediction mode and the block size/shape,filtering may be applied to the first reference sample line adjacent tothe current block but the filtering may not be applied to the second andsubsequent reference sample line around the current block.Alternatively, the filtering may be applied only to one reference sampleline. For example, the filtering may be applied only to either a leftreference sample line or an upper reference sample line. Which referencesample line is subjected to filtering may be determined depending on atleast one of the shape, size, and intra prediction mode of the currentblock. The shape of the current block may be determined depending on asize comparison between the width and the height of the current block ora ratio of the width and the height.

The configured reference sample may be represented as ref[m, n], and asample obtained by applying a filter to the configured reference samplemay be represented as rec[m, n]. Herein, m or n may be a predeterminedinteger value representing a position of a sample. When a position of aleft upper side sample within the current block is (0, 0), a position ofa left upper side reference sample of the current block may be set to(−1, −1).

FIG. 7 is a diagram for describing a plurality of reconstructed samplelines.

A reference sample can be constructed by selecting one or morereconstructed sample lines adjacent to the current block. For example,in FIG. 7, one of the plurality of reconstructed sample lines may beselected so as to construct a reference sample.

For example, a particular reconstructed sample line of the plurality ofreconstructed sample lines may be fixedly or adaptively selected, or anarbitrary reconstructed sample line may be adaptively selected, in orderto construct a reference sample.

In another embodiment, to construct a reference sample, one or morereconstructed sample lines may be selected from the plurality ofreconstructed sample lines illustrated in FIG. 7, and the selectedreconstructed sample lines may be combined.

For example, as shown in Equation 1, a reference sample may beconstructed using a weighted average of reconstructed samples, in whichthe weights of the reconstructed samples differ according to thedistance between the reconstructed sample and the current block.

$\begin{matrix}{{{ref}\lbrack {{- 1}\ ,{- 1}} \rbrack} = {( {{{rec}\lbrack {{- 2},{- 1}} \rbrack} + {2{{Xrec}\lbrack {{- 1},{- 1}} \rbrack}} + {re{c\lbrack {{- 1},{- 2}} \rbrack}} + 2} ) \gg 2}} & \lbrack {{Equation}1} \rbrack\end{matrix}$ref[x, −1] = (rec[x, −2] + 3Xrec[x, −1] + 2) ≫ 2, (x = 0toH + W − 1)ref[−1, y] = (rec[−2, y] + 3Xrec[−1, y] + 2) ≫ 2, (y = 0toH + W − 1)

Alternatively, a reference sample may be constructed using at least oneof a mean value, a maximum value, a minimum value, a median value, and amode value of a plurality of reconstructed samples based on at least oneof the distance from the current block to the correspondingreconstructed sample and the intra prediction mode of the current block.

Alternatively, a reference sample may be constructed based on a change(change amount) between each of the sample values of the successivereconstructed samples. For example, a reference sample may beconstructed based on at least one of a determination of whether thevalues of two successive reconstructed samples differ by more than athreshold value and a determination of whether the values of successivereconstructed samples change continuously or discontinuously. Forexample, when the values of a rec[−1, −1] and a rec[−2, −1] differ bymore than a threshold value, the value of the ref[−1, −1] is determinedas having the value of the rec[−1, −1], or a value corresponding to aweighted average obtained by applying a predetermined weight to thevalue of the rec[−1, −1]. For example, each of the values of thesuccessive reconstructed samples changes by n as the distance betweenthe reconstructed sample and the current block decreases, and thus thevalue of ref[−1, −1] is represented as “ref[−1, −1]=rec[−1, −1]−n”.

In a different embodiment, referring to FIG. 7, two or morereconstructed sample lines may be selected to construct a referencesample. For example, two lines including a reconstructed sample line 1and a reconstructed sample line 2 may be fixedly selected, or four linesranging from a reconstructed sample line 1 to a reconstructed sampleline 4 may be selected to construct a reference sample.

Alternatively, two or more reconstructed sample lines may be adaptivelyselected to construct a reference sample. For example, one reconstructedsample line may be fixedly selected, and one or more reconstructedsample lines may be adaptively selected among the other reconstructedsample lines to construct a reference sample.

The fixedly selected reconstructed sample line may be predefined in theencoder/decoder. For the case where the fixedly selected reconstructedsample line is predefined, information on the fixedly selectedreconstructed sample line may not be signaled.

The information on the adaptively selected reconstructed sample line(s)may be signaled in the form of an indicator or index. The adaptivelyselected reconstructed sample line may be determined based on at leastone of coding parameters of the current block or a block neighboring thecurrent block. For example, the adaptively selected reconstructed sampleline may be determined based on at least one of the size/shape and intraprediction mode of the current block or the block neighboring thecurrent block. In this case, the information necessary for selection maynot be signaled.

A reference sample line may include one or more samples. For example,the reference sample line may include samples corresponding to a lengthequal to the width (that is, the horizontal dimension) or height (thatis, the vertical dimension) of the current block. As another example,the reference sample line may include samples corresponding to a lengththat is two times the width or height of the current block. As a furtherexample, the reference sample line may include samples corresponding toa length equal to N samples (N is 1, 2, 3, . . . ) plus two times thesum of the width and height of the current block. That is, the referencesample line may include reference samples corresponding to 2×(W+H)+N(where W and H are the width and height of the current block, and N isan integer of 1 or more).

The method of constructing a reference sample adjacent to an upper partof the current block and the method of constructing a reference sampleadjacent to a left part of the current block may differ. For example,the number of reference sample lines located above the current block andthe number of reference sample lines located to the left of the currentblock may differ. For example, the number of reference sample linesadjacent to the upper part of the current block may be one and thenumber of reference sample lines adjacent to the left part of thecurrent block may be two, according to at least one of the width orheight of the current block, and the intra prediction mode of thecurrent block. For example, the length of the reference sample lineabove the current block and the length of the reference sample linelocated to the left of the current block may differ. For example, thelength of the reference sample line may vary according to at least oneof the width or height of the current block and the intra predictionmode of the current block.

Each of the reference sample lines may have a different length. Forexample, referring to FIG. 7, the lengths of the reconstructed samplelines 2 to 4 may be longer than the reconstructed sample line 1 by alength corresponding to one or more samples.

The length of the reference sample line may be different for each of thereconstructed sample lines. For example, a reconstructed sample line nmay be longer or shorter than a reconstructed sample line n−1 by alength corresponding to m samples. In the example illustrated in FIG. 7,the reconstructed sample line n is longer than the reconstructed sampleline n−1 by a length corresponding to one sample.

As described above, decision information on whether to construct areference sample using only the nearest reference sample line or using aplurality of reference sample lines may be encoded/decoded. For example,the decision information may be encoded/decoded at the level of at leastone of a sequence, a picture, a slice, a tile, a CTU, a CU, a PU, and aTU. In addition, information on the availability of each of theplurality of reference sample lines may be signaled at a higher level.

At least one of the number, position, and configuration of thereconstructed sample lines used in the reference sample construction maybe differently set when the top boundary or the left boundary of thecurrent block corresponds to the boundary of at least one of a picture,a slice, a tile, and a coding tree block (CTB). For example, when two ormore reference sample lines are constructed, when the top boundary ofthe current block corresponds to the boundary of at least one of apicture, a tile, a slice, and a coding tree block (CTB), one referencesample line adjacent to the upper part of the current block may beconstructed. For example, one reference sample line may be configuredwhen the top boundary of the current block corresponds to the topboundary of a CTU, and otherwise, two or more reference sample lines maybe configured. In this case, since only one reference sample line at thetop boundary of the CTU is used, the size of a line buffer for storingdata of the reference samples of the reference sample line can bereduced.

When selecting a reference sample, availability determination andreference sample padding may be performed for a block containing thereference sample to be used. For example, when a block containing areference sample is available, the corresponding reference sample can beused. On the other hand, when a block containing a reference sample isnot available, the unavailable reference samples in the block may bepadded with one or more available neighboring reference samples.

When a reference sample is located outside the boundary of at least oneof a picture, a tile, a slice, or a coding tree block (CTB), thereference sample may be determined to be unavailable. When the currentblock is coded with constrained intra prediction (CIP), in the casewhere the block including the reference sample has been encoded/decodedin an inter prediction mode, the reference sample is determined to beunavailable.

FIG. 8 is a diagram for describing a process of replacing an unavailablesample with an available sample.

When it is determined that the reconstructed neighboring sample is notavailable, the unavailable sample may be replaced with a reconstructedneighboring sample, which is an available sample. For example, whenthere are both available samples and unavailable samples as illustratedin FIG. 8, one or more available samples can be used to replace one ormore unavailable samples.

The sample values of the unavailable samples may be replaced with thevalues of the available samples in a predetermined order. The availablesamples used to replace the unavailable samples may be available sampleslocated adjacent to the unavailable samples. When no available sample isadjacent to the unavailable sample, the earliest or closest availablesample may be used to replace the unavailable sample. The replacingorder of the unavailable samples may be, for example, from the bottomleft to the top right. Alternatively, the replacing order may be fromthe top right to the bottom left. Specifically, the replacing order maybe from the top left corner to the top right and/or to the bottom left.Alternatively, the replacing order may be from the top right and/or fromthe bottom left to the top left corner.

For example, filling the unavailable samples with the values ofavailable samples may start from the position 0, which is the bottomleft sample position. That is, the first four unavailable samples may befilled with a value of “a”, and the subsequent 13 unavailable samplesmay be filled with a value of “b”.

For example, the unavailable samples may be filled with a combined valueof the available samples. For example, the unavailable samples may befilled with an average value or an interpolated value of the availablesamples respectively adjacent to both ends of a line of the unavailablesamples. That is, the first four unavailable samples are filled with thevalue “a”, and the next 13 unavailable samples may be filled with theaverage of a value of “b” and a value of “c”, or may be filled byinterpolating the value “b” and the value “c”.

Alternatively, the 13 unavailable samples may be filled with anarbitrary intermediate value between the sample values “b” and “c” ofthe available samples. In this case, the unavailable samples may befilled with different respective values. For example, as the distance ofan unavailable sample to the available sample having the value “a”decreases, the unavailable sample will be filled with a value that iscloser to the value “a”. For example, the closer an unavailable sampleis to an available sample having the value “b”, the closer the valuethat fills the unavailable sample is to the value “b”. That is, thevalue of an unavailable sample may be determined based on the distancebetween the unavailable sample and the available sample having the value“a” or “b”. To replace unavailable samples with available samples, oneor more replacement methods including the methods described above may beadaptively used. The method of replacing unavailable samples withavailable samples may be signaled as information contained in abitstream, or may be predetermined in the encoder/decoder.Alternatively, a replacement method may be derived according to apredetermined determination method. For example, the replacement methodmay be determined based on the difference between the values “a” and “b”or based on the number of unavailable samples. More specifically, thereplacement method may be determined by comparing the difference betweenthe values of two available samples with a threshold value and/or bycomparing the number of unavailable samples with a threshold value. Forexample, when the difference between the values of the two availablesamples is greater than the threshold value, and/or when the number ofunavailable samples is greater than the threshold value, the unavailablesamples may be replaced to have different values from each other. Theselection of the method of replacing unavailable samples with availablesamples may be performed on a per-predetermined-unit basis. For example,the replacement may be selected on a per-video basis, a per-sequencebasis, a per-picture basis, a per-slice basis, a per-tile basis, aper-coding-tree-unit (CTU) basis, a per-coding-unit (CU) basis, aper-prediction-unit (PU) basis, a per-transform-unit (TU) basis, or aper-block basis. At this time, the selection of the method of replacingunavailable samples with available samples may be determined based onthe information signaled on a per-predetermined-unit basis or may bederived on a per-predetermined-unit basis. Alternatively, the selectionmethod for the replacement methods may be predetermined in theencoder/decoder.

When a reference sample is located at a predetermined position, paddingmay be automatically performed without determining whether a blockincluding the reference sample is available or not. For example,referring to FIG. 7, when the position (x, y) of the top left cornersample of the current block is (0, 0), sample availability may not bedetermined for samples located at (x, y) in which the x coordinate orthe y coordinate is equal to or greater than W+H (x=W+H or greater ory=W+H or greater), and the samples may be padded with neighboringreference samples.

For example, a sample ref[W+H, −2] may be padded with the value of asample ref[W+H−1, −2] without performing the availability determinationon the sample ref[W+H, −2]. As another example, a sample ref[W+H, −3]may be padded with the value of a sample ref[W+H−1, −3] withoutperforming the availability determination on the sample[W+H, −3]. Thatis, the padding may be performed on the samples located at positions (x,y: x is equal to or greater than W+H or y is equal to or greater thanW+H) by using the closest sample on the same sample line withoutperforming the availability determination thereon.

When the position of the top left corner sample of the current block is(0, 0), for samples located at positions (x, y: x is equal to or greaterthan W and is less than W+H) among the samples located above the currentblock, the availability determination will be performed, and then thepadding will be performed according to the result of the availabilitydetermination. For samples located at positions (x, y: y is equal to orgreater than H and is less than W+H) among the samples located to theleft of the current block, the availability determination will beperformed, and the padding will be performed according to theavailability determination.

For example, when the position of the top left corner sample of thecurrent block is (0, 0), for samples corresponding to rec[x, −1] (xranges from −1 to W+H−1) and/or samples corresponding to rec[−1, y](yranges from 0 to H+W−1), the availability determination and the paddingmay be performed.

For the padding, a plurality of reference sample lines may be used. Forexample, when the padding is performed on a first reference sample lineadjacent to (that is, the closest to) the current block, a secondreference sample line, which is the second closest to the current block,may be used. For example, the padding may be performed according toEquation 2. That is, the sample values of the first reference sampleline may be derived by using the weighted average of samples selectedfrom the first reconstructed sample line and the second reconstructedsample line. In this case, the selected reconstructed sample may be onelocated at a current sample position or at a position adjacent to thecurrent sample position.

ref[x,−1]=(rec[x,−2]+3×rec[x,−1]+2)>>2, (x=0˜H+W−1)  [Equation 2]

Filtering may be performed on one or more reference samples among thesamples constructed as above. The filtering may be adaptively performedbased on at least one of the intra prediction mode of the current block,the size of the current block, and the shape of the current block. Forexample, at least one of a determination of whether to apply filtering,a filter type, a filter strength, and a filter coefficient may beadaptively determined.

For example, whether to apply the filtering may be determined for eachof the plurality of reference sample lines. For example, the filteringmay be applied to the first reference sample line adjacent to thecurrent block, and may not be applied to the second reference sampleline. For example, both a filtered value and an unfiltered value may beused for the same reference sample.

For example, at least one of a 3-tap filter, a 5-tap filter, a 7-tapfilter, and an N-tap filter may be selectively applied according to atleast one of the intra prediction mode of the current block, the size ofthe current block, and the shape of the current block. In this case, Nis a positive integer.

For example, filters having different shapes may be selectively usedaccording to at least one of the intra prediction mode, the size, andthe shape of the current block. FIGS. 9A-9D illustrates various filtershapes.

The shape of the current block may be determined by comparing the width(horizontal dimension) of the current block with the height (verticaldimension) of the current block. For example, at least one of a decisionof whether to apply a filter, a filter type, a filter strength, and afilter coefficient may be adaptively determined according to whether thecurrent block is a horizontally oblong block or a vertically oblongblock. Alternatively, at least one of a decision of whether to applyfiltering, a filter type, a filter strength, and a filter coefficientmay be adaptively determined according to whether the current block is arectangular block or a square block.

Intra prediction for the current block may be performed based on thederived intra prediction mode and the constructed reference sample.

For example, non-directional intra prediction may be performed for thecurrent block. The mode of the non-directional intra prediction may beat least one of a DC mode, a planar mode and an LM mode.

For the DC mode, prediction may be performed using the average value ofone or more reference samples among the constructed reference samples.In this case, filtering may be applied to one or more prediction samples(also referred to as predicted samples) located at the boundary of thecurrent block. The DC prediction may be adaptively performed based on atleast one of the size of the current block and the shape of the currentblock. Further, the range of the reference samples used in the DC modecan be determined based on at least one of the size and the shape of thecurrent block.

FIGS. 10A-10D are diagrams describing intra prediction according to theshapes of the current block.

For example, when the current block is a square block, as illustrated inFIG. 10A, DC prediction may be performed by using the average value ofthe reference sample located above the current block and the referencesample located to the left of the current block.

For example, when the current block is a non-square block, neighboringsamples adjacent to the left end and the upper end of the current blockmay be selectively used. When the current block is a rectangular block,as illustrated in (FIG. 10B, the prediction may be performed using theaverage value of the reference samples adjacent to a longer side amongthe left side and the upper side of the current block.

For example, when the size of the current block corresponds to apredetermined size or falls within a predetermined range, apredetermined number of reference samples, among the reference sampleslocated above or to the left of the current block, are selected, and theprediction is performed using the average value of the selectedreference samples. The predetermined size may be a fixed size of N×M,which is preset in the encoder/decoder. In this case, N and M areintegers greater than 0, and N and M may be the same or different fromeach other. The predetermined range may mean a threshold value forselecting the reference samples for prediction of the current block. Thethreshold value may be set with at least one of a minimum value and amaximum value. The minimum value and/or the maximum value may be a fixedvalue or fixed values preset in the encoder/decoder, or a variable valueor variable values that is/are encoded and then signaled by the encoder.

For example, one or more average values may be used to perform theprediction. When the current block is a square block or a non-squareblock, at least one of a first average value or a second average valuemay be used, in which the first average value is the average of thereference samples located above the current block and the second averagevalue is the average of the reference samples located to the left of thecurrent block. The DC prediction value of the current block may be thefirst average value or the second average value. Alternatively, the DCprediction value of the current block may be a weighted sum obtained byweighting the first average value and the second average value. Forexample, the weights for the first and second average values may be thesame (that is, 1:1).

According to the above method, a shift operation can be used tocalculate all of the DC values. For example, the method can be used evenfor the case where a sample length, which represents the width, theheight, or the sum of the width and height of the current block, is notthe power of two. The method may be applied to both luma DC predictionand chroma DC prediction. Alternatively, the method may be appliedeither to luma DC prediction or to chroma DC prediction.

For example, when the current block is a non-square block, theprediction may be performed based on either the width or the height ofthe current block. For example, a predicted value may be obtained bydividing the sum of the values of the upper reference sample and theleft reference sample by the length of a longer side (namely, the widthor the height) of the current block. In this case, the divisionoperation using the value corresponding to the longer one among thewidth and the height may be performed by a shift operation.

For example, the DC prediction may be performed using a plurality ofreference sample lines. For example, the prediction may be performedusing two reference sample lines, as illustrated in FIG. 100.

For example, the average value of the reference samples included in thetwo reference sample lines may be determined as the DC prediction valueof the current block.

Alternatively, different weights may be applied to the reference samplesof the first adjacent line and the reference samples of the secondadjacent line of the current block. For example, a weighted average ofeach sample in the first reference sample line and each sample in thesecond reference sample line is calculated by applying the weights 3:1to each sample in the first reference sample line and each sample in thesecond reference sample line (that is, (3×the first line referencesample+the second line reference sample+2)>>2), and the average of theweighted averages may be determined as the DC prediction value of thecurrent block. Alternatively, the resultant value of ((3×the first linereference sample−the second line reference sample)>>1) may be obtained,and the average of these values may be determined as the DC predictionvalue of the current block. The weights are not limited to the aboveexample, and any weights may be used. In this case, the closer to thecurrent block the reference sample line is, the larger the weight thatis applied to the reference sample line. The number of reference samplelines that can be used is not limited to two, and three or morereference sample lines may be used for prediction.

For the planar mode, prediction may be performed with a weighted sum asa function of the distance from at least one reference sample to anintra prediction target sample located in the current block.

Filtering may be performed on reference samples of the current block orprediction samples (that is, predicted samples) of the current block.For example, after filtering is applied to reference samples, planarprediction may be performed, and then filtering may be performed on oneor more prediction samples. Among the prediction samples, filtering maybe performed on samples in one, two, or N sample lines located at thetop boundary or the left boundary of the current block.

90 To perform the planar prediction, a weighted sum of one or morereference samples may be used. For example, five reference samples maybe used, as illustrated in FIG. 10D. For example, to generate aprediction sample for a target position [x, y], the reference samplesr[−1, −1], r[x, −1], r[−1, y], r[W, −1], and r[−1, H] may be used. Inthis case, W and H are the width and the height of the current block,respectively. For example, prediction samples pred[x, y] can begenerated using Equation 3. In Equation 3, a, b, c, d, and e representweights. N may be log₂(a+b+c+d+e).

pred[x,y]=(a×r[−1,−1]+b×r[x,−1]+c×r[−1,y]+d×r[W,−1]+e×r[−1,H])>>N  [Equation3]

As another example, the planar prediction may be performed using aplurality of reference sample lines. For example, the planar predictionmay be performed using a weighted sum of two reference sample lines. Asanother example, the planar prediction may be performed using a weightedsum of reference samples in the two reference sample lines. In thiscase, the reference samples selected from the second reference sampleline may be samples adjacent to the reference samples selected from thefirst reference sample line. That is, when the reference sample locatedat the position (−1, −1) is selected, the reference sample located atthe position (−2, −2) may be selected. The planar prediction may beperformed by calculating a weighted sum of the selected referencesamples, and in this case the same weights as those used for the DCprediction may be used.

A directional prediction mode refers to at least one of a horizontalmode, a vertical mode, and an angular mode having a predetermined angle.

In the horizontal mode or the vertical mode, prediction is performedusing one or more reference samples arranged in a linear direction,i.e., in the horizontal direction or the vertical direction. A pluralityof reference sample lines may be used. For example, when two referencesample lines are used, prediction may be performed using two referencesamples arranged in a horizontal line or a vertical line. Similarly,when N reference sample lines are used, N reference samples in ahorizontal line or a vertical line may be used.

For the vertical mode, the statistics of a first reference sample (e.g.,r[x, −1]) on a first reference sample line and a second reference sample(e.g., r[x, −2]) on a second reference sample line may be used toperform the directional prediction.

For example, the predicted value of the vertical mode can be determinedby calculating the result value of (3×r[x, −1]+r[x, −2]+2)>>2.Alternatively, the predicted value of the vertical mode can bedetermined by calculating the result value of (3×r[x, −1]−r[x,−2]+1)>>1. In yet another alternative, the predicted value of thevertical mode can be determined by calculating the value of (r[x,−1]+r[x, −2]+1)>>1.

For example, the change between each of the sample values on thevertical line may be considered. For example, the predicted value of thevertical mode can be determined by calculating the result value of (r[x,−1]+(r[x, −1]−r[x, −2])>>1). In this case, N may be an integer equal toor greater than 1. As N, a fixed value may be used. Alternatively, N mayincrease with an increase in the y coordinate of a prediction targetsample. For example, N=y+1.

Even for the horizontal mode, one or more methods used for the verticalmode can be used.

For an angular mode of a certain angle, prediction may be performedusing one or more reference samples arranged in an oblique directionfrom an intra prediction target sample of the current block, or one ormore samples neighboring the reference samples located in the obliquedirection. In this case, a total of N reference samples may be used,wherein N may be 2, 3, 4, 5, or 6. It is also possible to performprediction by applying at least one of an N-tap filter to the Nreference samples. Examples of the N-tap filter include a 2-tap filter,a 3-tap filter, a 4-tap filter, a 5-tap filter, and a 6-tap filter. Atthis time, at least one of the reference samples may be located abovethe current block and the rest may be located to the left of the currentblock. The reference samples located above the current block (or thereference samples located to the left of the current block) may belocated in the same line or in different lines.

According to another embodiment, intra prediction may be performed basedon position information. In this case, the position information may beencoded/decoded, and a reconstructed sample block located at theposition described above may be derived as an intra predicted block ofthe current block. Alternatively, a block similar to the current blockmay be searched for by the decoder, and the found block may be derivedas the intra predicted block of the current block. The searching for asimilar block may be performed in an encoder or a decoder. The range(search range) in which the search is performed may be limited to apredetermined range. For example, the search range may be limited toreconstructed sample blocks within a picture in which the current blockis included. Alternatively, the search range may be limited to a CTU inwhich the current block is included or to a predetermined CU. That is,location information-based intra prediction may be performed bysearching for a block similar to the current block among reconstructedsamples within a CTU. The searching may be performed using a template.For example, one or more reconstructed samples adjacent to the currentblock are taken as a template, and a CTU is searched for samples similarto the template.

The location information-based intra prediction may be performed whenthe CTU consists of only intra coding modes or when the luminance blockand the chrominance block have different partition structures. Forexample, for an inter prediction available slice (e.g., P or B slice),information indicating that the current CTU consists of only intracoding modes may be signaled. In this case, when the informationindicates that a current CTU consists of only intra coding modes, thelocation information-based intra prediction may be performed.Alternatively, when the luminance block and the chrominance block in thecurrent CTU have different partition structures (for example, whendual_tree or separate_tree is a value of 1), the locationinformation-based intra prediction may be available. On the other hand,when a CTU includes intra coding blocks and inter coding blocks or whenthe luminance block and the chrominance block have the same partitionstructure, location information-based intra prediction may not beavailable.

According to a further embodiment, inter color component intraprediction is performed. For example, it is possible to intra-predictchroma components from the corresponding reconstructed luma component ofthe current block. Alternatively, it is possible to intra-predict onechroma component Cr from the corresponding reconstructed chromacomponent Cb of the current block.

An inter color component intra prediction includes a color componentblock restructuring step, a prediction parameter deriving step, and/oran inter color component prediction execution step. The term ‘colorcomponent’ may refer to at least any one of a luma signal, a chromasignal, Red, Green, Blue, Y, Cb, and Cr. A prediction of a first colorcomponent can be performed by using at least any one of a second colorcomponent, a third color component, and a fourth color component. Thesignals of the color components used for the prediction may include atleast any one of an original signal, a reconstructed signal, a residualsignal, and a prediction signal.

When performing an intra prediction for a second color component targetblock, a sample of a first color component corresponding block thatcorresponds to the second color component target block, a sample of aneighbor block of the first color component corresponding block, or bothof the samples may be used. For example, when performing an intraprediction for a chroma component block Cb or Cr, a reconstructed lumacomponent block Y corresponding to the chroma component block Cb or Crmay be used.

When predicting the chroma components on the basis of the lumacomponent, the prediction may be performed according to Equation 4.

Pred_(C)(i,j)=α·rec_(L)′(i,j)+β  [Equation 4]

In Equation 4, Pred_(C)(i, j) represents a predicted chroma sample ofthe current block, and rec_(L)(i, j) represents a reconstructed lumasample of the current block. At this time, rec_(L)′(i, j) may be adown-sampled reconstructed luma sample. Parameters α and β may bederived by minimizing a regression error between the reconstructedneighboring luma sample and the reconstructed neighboring chroma samplearound the current block.

There are two modes for predicting the chroma components using the lumacomponent. The two modes may include a single-model mode and amultiple-model mode. The single-model mode may use one linear model whenpredicting the chroma components from the luma components for thecurrent block. The multiple-model mode may use two linear models.

In the multiple-model mode, the samples adjacent to the current block(that is, adjacent luma samples and adjacent chroma samples) may beclassified into two groups. That is, the parameters α and β for each ofthe two groups may be derived. Further, the luma samples of the currentblock may be classified according to the rules used for classificationof the luma samples adjacent to the current block.

For example, a threshold value for classifying the adjacent samples intotwo groups may be calculated. The threshold value may be calculatedusing an average value of the reconstructed adjacent luma samples.However, the calculation of the threshold value is not limited thereto.At least one of various statistical values recognized in the presentspecification may be used instead of the average value. When the valuesof the adjacent samples are larger than the threshold value, theadjacent samples may be classified into a first group. Otherwise, theadjacent samples may be classified into a second group.

Although it is described that the multiple-model mode uses two linearmodes in the embodiment described above, the present invention is notlimited thereto, and may cover other cases in which two or more linearmodels are used. When N linear models are used, samples may beclassified into N groups. To do so, N−1 threshold values may becalculated.

As described above, when predicting a chroma component from a lumacomponent, a linear model can be used. In this case, the linear modelmay include a simple linear model (hereinafter referred to as “LM1”), acomplex linear model (hereinafter referred to as “LM2”), and a complexfilter linear model (hereinafter, referred to as “LM3”). Parameters ofthe models described above may be derived by minimizing regression errorbetween the reconstructed luma samples around the current block and thecorresponding reconstructed chroma samples around the current block.

FIG. 11 is a diagram for describing “neighboring samples of a currentblock” (hereinafter referred to as “adjacent data set”) used to derivethe parameters of the models.

The adjacent data set for deriving the parameters of the LM1 may becomposed of a pair of samples comprising a luma sample and a chromasample in each of a line area B and a line area C illustrated in FIG.11. The adjacent data set for deriving the parameters of the LM2 and LM3may be composed of a pair of samples comprising a luma sample and chromasample in each of a line area B, a line area C, a line area E, and aline area F illustrated in FIG. 11.

However, the adjacent data set is not limited to the examples describedabove. For example, to cover various linear relationships between lumaand chroma samples in the current block, N adjacent data sets may beused for each mode. For example, N may be an integer of 2 or more, andspecifically 3.

The parameters of the linear model may be calculated using both an uppertemplate and a left template. Alternatively, there are two LM modes (anLM_A mode and an LM_L mode), and the upper template and the lefttemplate may be used in the LM_A mode and the LM_L mode, respectively.That is, in the LM_A mode, the linear model parameters may be obtainedusing only the upper template. When the position of the upper leftcorner sample of the current block is (0, 0), the upper template may beextended to a range from (0, −n) to (W+H−1, −n). In this case, n is aninteger equal to or greater than 1. That is, in the LM_L mode, thelinear model parameters may be obtained using only the left template.The left template may be extended to a range from (−n, 0) to (−n,H+W−1). In this case, n is an integer equal to or greater than 1.

A power of two numbers of samples can be used to derive the parametersof the linear model. When the current chroma block is a non-squareblock, the samples used to derive the parameters of the linear model maybe determined based on the number of samples on a shorter side, amongthe horizontal side and the vertical side of the current block.According to one embodiment, when the size of the current block is n×m(where n>m), m samples of the n adjacent samples adjacent to the topboundary of the current block may be selected, for example, byperforming sub-sampling uniformly. In this case, the number of samplesused to derive the parameters of the linear model may be 2m. As anotherexample, when the size of the current block is n×m (where n>m), msamples of the n adjacent samples adjacent to the top boundary of thecurrent block may not be used. For example, of the n samples, m samplesthat are farthest from the shorter one of the horizontal side and thevertical side of the current block may not be used. In this case, thenumber of samples used to derive the parameters of the linear model maybe n (n-m samples adjacent to the top boundary of the current block+msamples adjacent to the left boundary of the current block).

Alternatively, when performing an intra prediction fora chroma componentblock Cr, a chroma component block Cb may be used. Alternatively, whenperforming an intra prediction for a fourth color component block, atleast one of a first color component block, a second color componentblock, and a third color component, all of which correspond to thefourth color component block, may be used.

Whether or not to perform an inter color component intra prediction maybe determined based on at least any one of the size and the shape of acurrent target block. For example, when the size of the target block isequal to that of a coding tree unit (CTU), larger than a predeterminedsize, or within a predetermined size range, the inter color componentintra prediction for the target block can be performed. Alternatively,when the shape of the target block is a predetermined shape, the intercolor component intra prediction for the target block can be performed.The predetermined shape may be a square shape. In this case, when thetarget block has an oblong shape, the inter color component intraprediction for the target block may not be performed. Meanwhile, whenthe predetermined shape is an oblong shape, the embodiment describedabove inversely operates.

Alternatively, whether or not to perform an inter color component intraprediction for a prediction target block may be determined based on acoding parameter of at least any one block selected from among acorresponding block corresponding to the prediction target block andneighbor blocks of the corresponding block. For example, when thecorresponding block has been predicted through an intra predictionmethod in a constrained intra prediction (CI P) environment, an intercolor component intra prediction for the prediction target block may notbe performed. Alternatively, when the intra prediction mode of thecorresponding block is a predetermined mode, an inter color componentintra prediction for the prediction target block can be performed.Further alternatively, whether or not to perform an inter colorcomponent intra prediction may be determined on the basis of at leastany one of CBF information of the corresponding block and CBFinformation of the neighbor blocks thereof. The coding parameter is notlimited to a prediction mode of a block but various parameters that canbe used for encoding/decoding may be used.

The color component block restructuring step will be described below.

When predicting a second color component block by using a first colorcomponent block, the first color component block may be restructured.For example, when an image has an YCbCr color space and when a samplingratio of color components is one of 4:4:4, 4:2:2, and 4:2:0, the blocksizes of color components may differ from each other. Therefore, whenpredicting a second color component block using a first color componentblock having a different size from the second color component block, thefirst color component block may be restructured such that the blocksizes of the first color component and the second color component areequalized. The restructured block may include at least any one of asample in the first color component block that is a corresponding blockand a sample in a neighbor block of the first color component block.FIGS. 12A-12B are exemplary diagrams illustrating a process ofrestructuring a color component block.

In FIG. 12A, p1[x, y] represents a sample at a position (x, y) in thefirst color component block. In FIG. 12B, p1′[x, y] represents a sampleat a position (x, y) in the restructured block that is produced byrestructuring the first color component block.

When the first color component block has a larger size than the secondcolor component block, the first color component block is down-sampledto have a size equal to that of the second color component block. Thedown-sampling may be performed by applying an N-tap filter to one ormore samples (N is an integer equal to or larger than 1). For thedown-sampling, at least any one equation of Equation 5 to Equation 9 maybe used. In the case in which any one down-sampling method among variousdown-sampling methods is selectively used, an encoder may select onedown-sampling method as a predetermined down-sampling method. Forexample, the encoder may select a down-sampling method having optimaleffects. The selected down-sampling method is encoded and signaled to adecoder. The signaled information may be index information indicatingthe down-sampling method.

p1′[x,y]=(p1[2x,2y]+p1[2x,2y+1]+1)>>1  [Equation 5]

p1′[x,y]=(p1[2x+1,2y]+p1[2x+1,2y+1]+1)>>1  [Equation 6]

p1′[x,y]=(p1[2x−1,2y]+2xp1[2x,2y]+p1[2x+1,2y]+2)>>2  [Equation 7]

p1′[x,y]=(p1[2x−1,2y+1]+2*p1[2x,2y+1]+p1[2x+1,2y+1]+2)>>2  [Equation 8]

p1′[x,y]=(p1[2x−1,2y]+2*p1[2x,2y]+p1[2x+1,2y]+p1[2x−1,2y+1]+2*p1[2x,2y+1]+p1[2x+1,2y+1]+4)>>3  [Equation9]

The down-sampling method performed with respect to two or more samplesis not limited to any one of the examples of Equation 5 to Equation 9.For example, two or more samples used to calculate a down-sampled valuep1′[x, y] may be selected from a sample group consisting of a samplep1[2x, 2y] and neighbor samples thereof. The neighbor samples may beones selected among p1[2x−1, 2y−1], p[2x−1, 2y], p1[2x−1, 2y+1], p1[2x,2y−1], p1[2x, 2y+1], p1[2x+1, 2y−1], p1[2x+1, 2y], and p1[2x+1, 2y+1].The down-sampling can be performed by calculating the average or theweighted average of two or more samples.

Alternatively, the down-sampling may be performed in a manner ofselecting a specific sample among one or more samples. In this case, atleast any one of the following equations, Equation 10 to Equation 13,may be used for the down-sampling.

p1′[x,y]=p1[2x,2y]  [Equation 10]

p1′[x,y]=p1[2x,2y+1]  [Equation 11]

p1′[x,y]=p1[2x+1,2y]  [Equation 12]

p1′[x,y]=p1[2x+1,2y+1]  [Equation 13]

When the first color component block has a smaller size than the secondcolor component block, the first color component block is up-sampled tobe restructured such that the sizes of the first color component blockand the second color component block are equalized. In this case, theup-scaling is performed according to Equation 14.

$\begin{matrix}{{{p{1^{\prime}\lbrack {{2x},{2y}} \rbrack}} = {p{1\lbrack {x,y} \rbrack}}},} & \lbrack {{Equation}14} \rbrack\end{matrix}$ p1^(′)[2x + 1, 2y] = (p1[x, y] + p1[x + 1, y] + 1) ≫ 1,p1^(′)[2x, 2y + 1] = (p1[x, y] + p1[x, y + 1] + 1) ≫ 1,p1^(′)[2x + 1, 2y + 1] = (p1[x + 1, y] + p1[x, y + 1] + 1) ≫ 1

In the restructuring process, a filter may be applied to one or moresamples. For example, the filter may be applied to one or more samplesincluded in at least any one of the first color component block (i.e.corresponding block), neighbor blocks of the corresponding block, thesecond color component block (i.e. target block), and neighbor blocks ofthe target block.

In the reference sample restructuring step described above, an indicatorcorresponding to a predetermined reference sample line among a pluralityof reference sample lines may be signaled. In this case, in therestructuring process, the restructuring is performed using thepredetermined reference sample line corresponding to the signaledindicator. For example, when the indicator mrl_index has a value of 0,the reconstruction process is performed using the first and secondreference sample lines adjacent to a first color component correspondingblock. Alternatively, when the indicator mrl_index has a value of 1, thereconstruction process is performed using the second and third referencesample lines adjacent to the first color component corresponding block.Alternatively, when the indicator mrl_index has a value of 3, thereconstruction process is performed using the third and fourth referencesample lines adjacent to the first color component corresponding block.A reference sample line indicated by the indicator mrl_index may be usedfor a second color component target block.

In the restructuring process, when a boundary of the second colorcomponent block (target block) or a boundary of the first colorcomponent block (corresponding block) is a boundary of a predeterminedregion, the reference samples used for the restructuring may bedifferently selected. In this case, the number of reference sample linesat the upper side may differ from the number of reference sample linesat the left side. The predetermined region may be at least any one of apicture, a slice, a tile, a CTU, and a CU.

For example, when the upper boundary of the first color componentcorresponding block is the boundary of the predetermined region, thereference samples at the upper side may not be used for therestructuring but only the reference samples at the left side may beused for the restructuring. When the left boundary of the first colorcomponent corresponding block is the boundary of the predeterminedregion, the reference samples at the left side may not be used for therestructuring but only the reference samples at the upper side may beused for the restructuring. Alternatively, both of N reference samplelines at the upper side and M reference sample lines at the left sidemay be used for the restructuring, in which N may be smaller than M. Forexample, when the upper boundary corresponds to the boundary of thepredetermined region, N may be 1. Meanwhile, when the left boundarycorresponds to the boundary of the predetermined region, M may be 1.

Alternatively, the restructuring may be performed by using N referencesample lines at the upper side and M reference left sample lines at theleft side of the first color component corresponding block, regardlessof whether the boundary of the predetermined region is the upperboundary or the left boundary of the first color component block.

FIGS. 13A-13E is a diagram illustrating an embodiment performingrestructuring by using a plurality of upper-side reference sample linesand/or a plurality of left-side reference sample lines.

As illustrated in FIG. 13A, the restructuring may be performed usingfour upper-side reference sample lines and four left-side referencesample lines.

For example, when the upper boundary or the left boundary of the firstcolor component corresponding block is the boundary of the predeterminedregion, the number of the upper-side reference sample lines and thenumber of the left-side reference sample lines used for therestructuring may differ from each other. For example, as illustrated inFIGS. 13B to 13D, any of the following combinations may be used for therestructuring: two upper-side reference sample lines and four left-sidereference sample lines; one upper-side reference sample line and threeleft-side reference sample lines; and one upper-side reference sampleline and two left-side reference sample lines.

The number of reference sample lines used for the restructuring is notlimited to the above combinations. That is, N upper-side referencesamples lines and M left-side reference sample lines may be used inwhich N and M are equal to or different from each other. When both ofthe upper boundary and the left boundary of the corresponding blockcorrespond to the boundary of the predetermined region, N and M may beequal to each other. That is, N and M may be both 1. Alternatively, Nmay be set smaller than M under the same condition. This is because moreresources (memory) are required for the upper-side reference samplelines than for the left-side reference sample lines.

Alternatively, as illustrated in FIG. 13E, one or more reference sampleswithin a region having a vertical length and a horizontal length notlarger than those of the first color component corresponding block maybe used for the restructuring.

When performing the restructuring process, the reference samples of thefirst color component corresponding block may be differently setdepending on any one of the block size, the block shape, and the codingparameter of at least any one block selected among the first colorcomponent corresponding block, neighbor blocks thereof, the second colorcomponent target block, and neighbor blocks thereof.

For example, among samples in the first color component correspondingblock and the neighbor blocks thereof, samples in blocks whose encodingmode is an inter frame encoding mode are not used but only samples inblocks whose encoding mode is an intra encoding mode are used for therestructuring.

FIGS. 14A-14D are exemplary diagrams illustrating reference samples usedfor the restructuring in accordance with an intra prediction mode or acoding parameter of a corresponding block. The restructuring of thereference samples of the first color component block may be differentlyperformed in accordance with the intra prediction modes of the firstcolor component corresponding block. For example, when the intraprediction mode of the corresponding block is a non-angular mode, suchas a DC mode and a planar mode, or an angular mode in which both of theupper-side reference samples and the left-side reference samples areused, as illustrated in FIG. 14A, at least one sample group of theupper-side reference samples and the left-side reference samples is usedfor the restructuring. Alternatively, when the intra prediction mode ofthe corresponding block is an angular mode in which both of theupper-side reference samples and the upper right-side reference samplesof the corresponding block are used, as illustrated in FIG. 14B, therestructuring of the corresponding block is performed using at least onesample group of the upper-side reference samples and the upperright-side reference samples. Alternatively, when the intra predictionmode of the corresponding block is an angular mode in which both of theleft-side reference samples and the lower left-side reference samplesare used, as illustrated in FIG. 14C, the corresponding block may berestructured using at least any one sample group of the left-sidereference samples and the lower left-side reference samples.

Alternatively, the reconstructing of the reference samples of the firstcolor component corresponding block are differently performed accordingto the quantization parameter of at least one among the first colorcomponent corresponding block and the neighbor blocks thereof. Forexample, as illustrated in FIG. 14D, reference samples in an upper blockhaving a relatively small quantization parameter value QP among theneighbor blocks are used for performing the restructuring.

Alternatively, when the second color component target block has anoblong shape, reference samples disposed around a first color componentcorresponding block having a square shape are used for therestructuring.

Alternatively, when the second color component target block ispartitioned into two sub-blocks (for example, two 16×8-size sub-blocks)and when the first color component corresponding block is a 32×16-sizeblock, reference samples disposed around a 32×32-size block are used forthe restructuring of the corresponding block. In this case, as referencesamples of the first color component block corresponding to a second16×8-size sub-block disposed at a lower side among the partitioned twosub-blocks of the second color component target block, reference samplesaround a restructured 32×32-size block may be shared.

Hereinbelow, the prediction parameter deriving step will be described.

A prediction parameter can be derived using at least any one ofreference samples of the restructured first color componentcorresponding block and reference samples of the second color componentprediction target block. Hereinafter, the terms ‘first color component’and ‘first color component block’ may respectively refer to arestructured first color component and a restructured first colorcomponent block.

FIGS. 15A-15G are diagrams illustrating an exemplary restructured firstcolor component corresponding block when a second color componentprediction target block is a 4×4 block. In this case, the number ofreference sample lines may be N.

The prediction parameter may be derived using reference samples disposedat the upper side and the left side of the restructured first colorcomponent corresponding block or of the second color componentprediction target block as illustrated in the FIG. 15A.

For example, the prediction parameter can be derived by adaptively usingthe reference samples of the restructured first color component, on thebasis of the intra prediction mode of the first color componentcorresponding block. In this case, the reference samples of the secondcolor component can be adaptively used on the basis of the intraprediction mode of the first color component corresponding block.

When the intra prediction mode of the first color componentcorresponding block is a non-angular mode such as a DC mode or a planarmode, or an angular mode in which both of upper-side reference samplesand left-side reference samples are used, reference samples at the upperside and the left side of the first color component corresponding blockcan be used as illustrated in FIG. 15A.

When the intra prediction mode of the first color componentcorresponding block is a angular mode in which upper-side referencesamples are used, reference samples at the upper side of the first colorcomponent corresponding block may be used as illustrated in FIG. 15B or15C.

When the intra prediction mode of the first color componentcorresponding block is an angular mode in which left side referencesamples are used, reference samples at the left side of the first colorcomponent corresponding block may be used as illustrated in FIG. 15D or15E.

Alternatively, when the intra prediction mode of the first colorcomponent corresponding block is an angular mode, reference samples usedin each prediction mode can be used as reference samples of the firstcolor component. For example, when the intra prediction mode is avertical mode, reference samples illustrated in FIG. 15B may be used.When the intra prediction mode is a horizontal mode, reference samplesillustrated in FIG. 15D may be used. When the intra prediction mode isan up-right diagonal mode, reference samples illustrated in FIG. 15C maybe used. When the intra prediction mode is a down-left diagonal mode,reference samples illustrated in FIG. 15E may be used. When the intraprediction mode is a mode between the vertical mode and the up-rightdiagonal mode, reference samples illustrated in FIG. 15F may be used.When the intra prediction mode is an angular mode of a 45° diagonaldirection, upper right reference samples, lower left reference samples,or both are used as illustrated in FIG. 15G. Reference samples that aredifferently selected for each intra prediction mode are stored in aformat of a look-up table so as to be conveniently used.

The prediction parameter may be derived by adaptively using thereference samples of the first color component or the second colorcomponent in accordance with the size and/or the shape of the firstcolor component block and/or the second color component block.

For example, when the second color component target block has a 64×64size, 32, 16, or 8 reference samples among reference samples at theupper side or the left side of the first color component block or thesecond color component block may be used. As described above, when thesize of the second color component target block is a predetermined size,the reference samples of the first or second color component block maybe adaptively used. The predetermined size is not limited to the 64×64size, but it may be a size signaled through a bitstream or a sizederived on the basis of the coding parameter of a current block or aneighbor block thereof.

Alternatively, when the second color component target block has anoblong shape, reference samples adjacent to a longer side, which is avertical side or a horizontal side, of the second color component targetblock may be used. For example, when the target block has a block sizeof 32×8, reference samples at the upper side of the first colorcomponent or the second color component block may be used.

Alternatively, when the second color component target block has anoblong shape, reference samples around a square block can be used. Forexample, when the target block is a 32×8 block, reference samples arounda 32×32 block can be used.

The prediction parameter can be derived using reference samples aroundthe restructured first color component block and reference samplesaround the second color component block. The prediction parameter can bederived on the basis of any one of the factors including a correlation,a change, an average value, and a distribution of color components. Inthis case, any one of the methods of Least Squares (LS), Least MeanSquares (LMS), etc. may be used.

When deriving the prediction parameters through the LMS method, theprediction parameters may be a and b, α and β, or both. Predictionparameters that can minimize an error between the reference samples ofthe first color component and the reference samples of the second colorcomponent can be derived by Equation 15.

$\begin{matrix}{{E( {a,b} )} = {\sum\limits_{n = 0}^{N - 1}( {{p2_{n}} - ( {{{a \cdot p}1_{n}^{\prime}} + b} )} )^{2}}} & \lbrack {{Equation}15} \rbrack\end{matrix}$

In Equation 15, p2_(n) represents a reference sample of the second colorcomponent, and p1′_(n) represents a reference sample of the restructuredfirst color component. N is the number of used reference samplesarranged in a vertical direction or a horizontal direction, and a and brepresent prediction parameters.

In this case, a correlation between the reference samples can becalculated by Equation 16.

$\begin{matrix}{k = {{Max}( {0,{{BitDepth} + {\log 2(N)} - 15}} )}} & \lbrack {{Equation}16} \rbrack\end{matrix}$$L = {( {{\sum\limits_{y = 0}^{N - 1}{p{1^{\prime}\lbrack {{- 1},y} \rbrack}}} + {\sum\limits_{x = 0}^{N - 1}{p{1^{\prime}\lbrack {x,{- 1}} \rbrack}}}} ) \gg k}$$C = {( {{\sum\limits_{y = 0}^{N - 1}{p{2\lbrack {{- 1},y} \rbrack}}} + {\sum\limits_{x = 0}^{N - 1}{p{2\lbrack {x,{- 1}} \rbrack}}}} ) \gg k}$${LL} = {( {{\sum\limits_{y = 0}^{N - 1}{p{1^{\prime}\lbrack {{- 1},y} \rbrack}2}} + {\sum\limits_{x = 0}^{N - 1}{p{1^{\prime}\lbrack {x,{- 1}} \rbrack}2}}} ) \gg k}$${LC} = {( {{\sum\limits_{y = 0}^{N - 1}{p{1^{\prime}\lbrack {{- 1},y} \rbrack} \times p{2\lbrack {{- 1},y} \rbrack}}} + {\sum\limits_{x = 0}^{N - 1}{p{1^{\prime}\lbrack {x,{- 1}} \rbrack} \times p{2\lbrack {x,{- 1}} \rbrack}}}} ) \gg k}$

In Equation 16, BitDepth represents a bit depth. p1′ represent a sampleof the restructured first color component, and p2 represents a sample ofthe second color component. FIG. 16 is a diagram illustrating a sampleof a first color component and a sample of a second color component.

When there is a region with no reference sample in the process ofderiving a prediction parameter, the prediction parameter can be derivedusing only existing samples.

One or more prediction parameters can be derived. For example, a firstprediction parameter may be derived from reference samples having valuessatisfying a specific requirement among reference samples used to deriveprediction parameters. In addition, a second prediction parameter may bederived from referenced samples having values that do not satisfy thespecific requirement. The specific requirement may be a condition inwhich the value of a reference sample is less than a statistic figure(for example, an average value).

According to another embodiment of the present invention, a basicprediction parameter (default parameter) may be used instead of derivinga prediction parameter from values of reference samples. The defaultparameters may be predefined in the encoder and the decoder. Forexample, the prediction parameters a and b may be respectively 1 and 0.

Alternatively, when deriving prediction parameters from referencesamples, the derived prediction parameters may be encoded and decoded.

When performing an inter color component prediction among colorcomponents Y, Cb, and Cr, prediction parameters used to predict colorcomponents Cb and Cr can be derived from a color component Y. Predictionparameters used to predict a color component Cr can be derived from acolor component Cb. Alternatively, as prediction parameters forpredicting a color component Cr, the prediction parameters that havebeen derived from a color component Y to predict a color component Cbcan be used as they are, instead of deriving new prediction parametersfor a prediction of the color component Cr.

Hereinbelow, the inter color component prediction execution step will bedescribed.

As described above, after prediction parameters are derived, an intercolor component intra prediction can be performed using at least any oneof the derived prediction parameters.

For example, a prediction of a second color component target block canbe performed by applying the derived prediction parameter to areconstructed signal of the restructured first color component,according to Equation 17.

p2[x,y]=a×p1′[x,y]+b  [Equation 17]

In Equation 17, p2[x, y] represents a prediction block of the secondcolor component target block. p1′[x, y] represents the first colorcomponent block or the restructured first color component block.

Alternatively, the prediction of the second color component target blockcan be performed by applying the derived prediction parameter to aresidual signal of the restructured first color component, according toEquation 18.

p2[x,y]=p2_pred[x,y]+a×p1′_residual[x,y]  [Equation 18]

In Equation 18, p1′_residual represents a residual signal of the firstcolor component and p2_pred represents a prediction signal obtained byperforming an intra prediction with respect to the second colorcomponent target block.

When the number of the derived prediction parameters is one or more, oneor more prediction parameters may be applied to the reconstructed sampleof the first color component. For example, when the reconstructed sampleof the first color component satisfies a specific requirement, the intercolor component intra prediction may be performed by applying the firstprediction parameter derived from the reference samples that satisfy thespecific requirement. Meanwhile, when the reconstructed sample of thefirst color component does not satisfy the specific requirement, theinter color component intra prediction may be performed by applying thesecond prediction parameter derived from the reference samples that donot satisfy the specific requirement. The specific requirement means acondition that the value of a reference sample is less than a statisticfigure (for example, an average value) of the reference samples of thefirst color component.

The inter color component prediction method may be used in an interprediction mode. For example, when performing the inter prediction onthe current block, inter prediction is performed for a first colorcomponent, and inter color component prediction or prediction combininginter prediction and inter color component prediction may be performedfor a second color component. For example, the first color component maybe a luma component, and the second color component may be a chromacomponent.

The inter-color component prediction may be performed using theprediction sample or the reconstructed sample of the luminancecomponent. For example, after the inter prediction for the luminancecomponent is performed, prediction for a color component may beperformed by applying inter-color component prediction parameters to theprediction sample resulting from the inter prediction of the luminancecomponent. Here, the prediction sample refers to a sample that hasundergone at least one of motion compensation, motion refinement,overlapped block motion compensation (OBMC), and bi-directional opticalflow (BIO).

In addition, the inter color component prediction may be performedadaptively according to the coding parameters of the first colorcomponent. For example, it is possible to determine whether to performinter color component prediction according to CBF information of thefirst color component. The CBF information may be information indicatingwhether a residual signal exists or not. That is, when the CBF of thefirst color component is 1, inter color component prediction may beperformed on the second color component. When the CBF of the first colorcomponent is 0, inter color component prediction may not be performed onthe second color component, and the inter prediction may be performed onthe second color component. Alternatively, a flag indicating whether ornot to perform the inter color component prediction may be signaled.

When coding parameters of the first color component satisfies apredetermined condition, a flag indicating whether to perform theinter-color component prediction may be signaled. For example, when theCBF of the first color component is 1, the flag may be signaled todetermine whether to perform inter-color component prediction.

When performing inter-color component prediction for the second colorcomponent, an inter motion prediction or compensation value for thesecond color component may be used. For example, inter motion predictionor compensation for the second color component may be performed usinginter prediction information of the first color component. In addition,prediction may be performed by calculating the weighted sum of theinter-color component prediction value for the second color componentand the inter motion compensation value.

According to another embodiment of the present invention, representativesample-based intra prediction may be performed. When performing therepresentative sample-based intra prediction, prediction may beperformed using at least one of block partitioning, representativesample determination, representative sample prediction, transformationand quantization, intra prediction using a representative sample, andreconstruction.

A current block may be divided into one or more sub-blocks. The size ofthe current block and/or the sub-block is represented by W×H in which Wand H are predetermined integers. For example, the size of the currentblock and/or the sub-block may be any one selected from among CTU, CU,signaling unit (SU), QTMax, QTMin, BTMax, BTMin, 4×4, 8×8, 16×16, 32×32,64×64, 128×128, 4×8, 8×16, 16×8, 32×64, 32×8, 4×32, etc. In this case,QTMax and QTMin respectively represent the maximum and minimum sizes ofa block that can be produced through quad-tree partitioning. Among thosesizes, BTMax and BTMin respectively represent the maximum and minimumsizes of a block that can be produced through binary-tree partitioning.

The size of the sub-block varies depending on the size of the currentblock. For example, the size of the sub-block is equal to the size(width or height) of the current block divided by N. In this case, N maybe a positive integer and more specifically at least one of 2, 4, 8, 16,32, and 64. For example, when the size of the current block is 32×32 andeach of the width and height of the current block is divided by 4 (thatis, N is 4), the size of the sub-block may be 8×8.

The size of the sub-block may be determined depending on the codingparameter of a neighboring block. For example, the size of the sub-blockmay be determined depending on whether a neighboring block is an intracoding block or an inter coding block. Alternatively, the size of thesub-block may be determined depending on the intra prediction mode of aneighboring block. Alternatively, the size of the sub-block may bedetermined depending on whether or not a neighboring block ispartitioned.

At least one of the divisible size of the current block, the size of thesub-block, and the value of the size of the current block divided by Nmay be a predetermined fixed size or value.

For example, when the dividable size of the current block is a fixedsize of 16×16, in a case where the size of the current block is 16×16,the current block may be divided into sub-blocks.

For example, when the size of the sub-block is fixed to a size of 4×4,the size of the sub-block is required to be always 4×4 regardless of thesize of the current block.

For example, assuming that the divisible size of the current block is aCTU and the value of N is 4, when the size of the current blockcorresponds to a CTU, the current block may be divided into sub-blocksin a manner that each of the width and height of the current block isdivided by 4.

One or more sub-blocks of the sub-blocks may be divided into smallersub-blocks. For example, when the size of the current block is 32×32 andthe size of the sub-block is 16×16, the sub-block may be divided intosmaller sub-blocks of 8×8, 4×4, 16×8, 4×16, etc.

At least one of the divisible size of the current block, the size of thesub-block, and the value of the size of the current block divided by Nmay be determined through entropy encoding/decoding. Information of atleast one of the divisible size of the current block, the size of thesub-block, and the value of the size of the current block divided by Nmay be predefined in an encoder and a decoder. Alternatively, theinformation may be signaled at a block level or at a higher level than ablock. The higher levels include a video, a sequence, a picture, aslice, a tile, a CTU, and a CU.

One or more samples in the current block or the sub-block may bedetermined as a representative sample.

The representative sample may be one or more samples located in a blockin which the block may be the current block or the sub-block.

FIGS. 17A-17D are diagrams illustrating an exemplary method ofdetermining a representative sample.

Diagrams denoted by FIGS. 17A and 17D show examples of a current block,and diagrams denoted by FIGS. 17B and 17C show examples of sub-blocksresulting from division of a current block.

For example, referring to the diagram denoted by FIG. 17A, a samplelocated at the lower right corner of the current block may be determinedas a representative sample.

Alternatively, referring to the diagram denoted by FIG. 17B, a samplelocated at the center of the current block may be determined as arepresentative sample.

Alternatively, referring to the diagram denoted by FIG. 17C, two sampleslocated respectively at the lower right corner and the center of thecurrent block may be determined as representative samples.

The value of the representative sample may be at least one of theoriginal sample value, the predicted sample value, and the reconstructedsample value corresponding to the position which has been described withreference to the diagrams denoted by FIGS. 17A-17C.

The position of the representative sample may be a fixed position. Forexample, the position may be the lower right corner of a block. In thiscase, the information of the position of the representative sample needsnot be signaled.

Alternatively, information indicating the position of the representativesample may be signaled.

Alternatively, the number of representative samples and/or the positionsof the representative samples may be determined based on at least one ofthe intra prediction mode of the current block (i.e., whether it is adirectional mode or a non-directional mode and/or a specific directionin the case of the directional mode), the size of the current block, andthe shape of the current block.

The value of the representative sample is a statistical value of one ormore samples in the vicinity of the position shown in the diagramsdenoted by FIGS. 17A-17C.

For example, when the position of the representative sample isdetermined to be D as illustrated in the diagram denoted by FIG. 17D, astatistical value of two or more samples selected from among samples A,B, C, and D (i.e., a sample located at the designated position D andneighboring samples located around the designated position D) may bedetermined as the representative sample value. In this case, examples ofthe statistical value include a mean value, a median value, a maximumvalue, a minimum value, a mode value, and a weighted average. Thepositions of the neighboring samples to be used are determined dependingon at least one of the intra prediction mode, size and shape of thecurrent block.

For example, when the intra prediction mode is a vertical mode, thesamples B and D may be used. For example, when the size of a block isequal to or larger than a predetermined size, all the samples A throughD may be used. For example, when a block has a vertically elongatedrectangular shape, the samples B and D may be used.

For example, when the intra prediction mode is a vertical mode, thesamples C and D may be used. For example, when the size of a block isequal to or smaller than a predetermined size, all the samples A throughD may be used. For example, when a block has a vertically elongatedrectangular shape, the samples C and D may be used.

For example, when the position of the representative sample isdetermined to be D in the diagram denoted by FIG. 17D, the average value(i.e., (A+B+C+D+2)>>2) of the samples A, B, C, and D is determined asthe representative sample value. Alternatively, the weighted sum (i.e.,(B+2*D+C+2)>>2) of the samples B, C, and D may be determined as therepresentative sample value. Alternatively, the median value of thesamples A, B, C, and D may be determined as the representative samplevalue.

One or more operations among prediction, transformation/inversetransformation, and quantization/dequantization are performed on thedetermined representative samples.

The prediction for the representative sample may be performed using oneor more reconstructed reference samples around the current block.

FIG. 18 is a diagram illustrating an exemplary method of performingprediction for a representative sample.

FIG. 18 illustrates four blocks including a current block positioned ata lower right corner, a left neighboring block, an upper neighboringblock, and an upper left neighboring block. In FIG. 18, a black dot inthe current block represents the representative sample, and gray dots inthe respective neighboring blocks represent reference samples. In thefollowing description, the upper neighboring block or the referencesample within the upper neighboring block is represented by “A”, theleft neighboring block or the reference sample within the leftneighboring block is represented by “L”, and the upper left neighboringblock or the reference sample within the upper left neighboring block isrepresented by “AL”.

For example, as illustrated in FIG. 18, prediction for the value of therepresentative sample R located at the lower right corner positionwithin the current block may be performed using at least one of thereconstructed reference samples within the upper neighboring block A,the left neighboring block L, or the upper left neighboring block AL.The reconstructed reference sample may be a sample positioned at thelower right corner within a reconstructed neighboring block.Alternatively, it may be a co-located sample within a reconstructedneighboring block. That is, within the reconstructed neighboring block,a sample located at a position corresponding to the position of therepresentative sample within the current block is referred to as theco-located sample. In this case, the representative sample value may bethe original sample value of the sample at the position. For example,when using reconstructed reference samples within the upper neighboringblock A and the left neighboring block L, a predicted representativesample value “Pred_R” which is the predicted value for therepresentative sample is derived by Equation 19 described below.

Pred_R=(A+L+1)>>1  [Equation 19]

In Equation 19, A represents the value of a reconstructed referencesample within the upper neighboring block A and L represents the valueof a reconstructed reference sample within the left neighboring block.

FIGS. 19A-19B are diagrams illustrating another exemplary method ofperforming prediction for a representative sample.

In the embodiment illustrated in FIGS. 19A-19B, a current block isdivided into 16 sub-blocks. The left, upper, and upper left neighboringblocks of the current block have the same size as the sub-block. Theabove description associated with FIG. 18 is appropriately referred tofor understanding of determination of positions of representativesamples and reference samples.

For example, referring to a diagram denoted by FIG. 19A, lower rightcorner samples within the respective sub-blocks within the current blockare determined as representative samples. In this case, referring to adiagram denoted by FIG. 19B, a block is generated by gathering therepresentative samples within the respective sub-blocks. In addition,reference samples existing in the vicinity of the current blockillustrated in the diagram denoted by FIG. 19A are used as reconstructedreference samples for the newly generated block (hereinafter, referredto as a representative sample block) composed of the representativesamples as illustrated in the diagram denoted by FIG. 19B. In performingprediction for the block composed of the representative samples shown inthe diagram denoted by FIG. 19B, a directional prediction or anon-directional prediction is performed using a reconstructed referencesample block composed of reference samples existing in the vicinity ofthe current block. In this case, the reference samples are sampleswithin neighboring blocks having the same x coordinate value or the samey coordinate value as the representative sample.

Alternatively, the average value of reference samples adjacent to thecurrent block may be used as a prediction value of the representativesample. For example, a DC mode prediction value for the current blockcan be used as the prediction value of the representative sample.Alternatively, the block (i.e., representative sample block) composed ofthe representative samples as shown in the diagram indicated by FIG. 19Bmay be used as a current block, and the method according to the presentinvention may be applied. In this case, the representative sample blockcan be reconstructed.

A representative sample residual signal corresponding to a differencebetween the value of the representative sample and the prediction valueof the representative sample may be entropy-encoded or entropy-decoded.

Transformation/inverse transformation or quantization/dequantization maybe performed on the representative sample residual signal. In this case,the type of the transformation/inverse transformation may vary dependingon the prediction mode of the representative sample.

After reconstructing the representative sample using the predictionvalue and the residual signal of the representative sample, intraprediction for the current block is performed on the basis of thereconstructed representative sample.

The reconstructed representative sample refers to a value obtained byperforming dequantization and/or inverse transformation on therepresentative sample residual signal to generate an operation value andthen adding the predicted representative sample (the prediction value ofthe representative sample) to the operation value. Hereinafter, therepresentative sample means the reconstructed representative sample.

The intra prediction for the current block may be performed using atleast one of the reconstructed representative sample and the referencesamples adjacent to the current block.

The intra prediction may be performed using interpolation of thereconstructed representative sample and each of the reference sample.

FIG. 20 is a diagram illustrating an exemplary method of generatingright-column prediction samples and bottom-row prediction samples of thecurrent block by using the reconstructed representative sample and thereference samples.

FIG. 20 illustrates four blocks including a current block which is alower right block in the diagram, a left neighboring block, an upperneighboring block, and an upper left neighboring block. In FIG. 20, ablack dot in the current block represents a representative sample, andgray dots in the respective neighboring blocks represent referencesamples.

For example, as illustrated in FIG. 20, right-column prediction samples(hatched dots) and bottom-row prediction samples (hatched dots) of thecurrent block by performing interpolation of the representative samplepositioned at the lower right corner and each of the reference samples.For example, when the current block has a size of 8×8, the bottom-rowprediction samples (the predicted sample values at the bottom row) arecalculated as (a*L+b*Re+4)>>3, in which “a” and “b” represent weightsthat vary with positions of samples to be predicted, L represents alower left reference sample, Re represents a representative samplepositioned at a lower right corner within the current block.

The prediction samples for the respective samples within the block canbe generated by using the reference samples and one or more predictionsamples of the bottom-row prediction samples and the right-columnprediction samples.

FIG. 21 is a diagram illustrating an exemplary method of performingprediction by using the reference samples and the right-column orbottom-row prediction samples.

FIG. 21 illustrates an embodiment in which samples within a currentblock are predicted using right-column and bottom-row prediction samples(corresponding to hatches dots) generated through the method of FIG. 20.

As illustrated in FIG. 21, prediction for the samples within the currentis performed using an interpolation method. For example, when thecurrent block has a size of 8×8, the prediction samples (the predictedsample values) are calculated as (a*L+b*R+c*A+d*B+8)>>4, in which “a”,“b”, “c”, and “d” represent weights that vary with positions of samplesto be predicted, L represents a reference sample on the left side of thecurrent block, R represents a prediction sample on the right columnwithin the current block, A represents a reference sample above thecurrent block, and B represents a prediction sample on the bottom-rowwithin the current block.

In order to predict the samples within the current block, directionalprediction or non-directional prediction is performed. In this case,directional intra prediction may be performed from the right-column andbottom-row prediction samples. Alternatively, bi-directional intraprediction may be performed from the reference samples and theright-column and bottom-row prediction samples. A prediction direction(hereinafter, referred to as a second direction) for performing thedirectional intra prediction from the right-column and bottom-rowprediction samples is determined depending on a prediction direction(hereinafter, referred to as a first direction) for performing thedirectional intra prediction from the reference samples. For example,the second direction is at an angle of 180° with respect to the firstdirection. Alternatively, the second direction may be determinedirrespective of the first direction. For example, information on thefirst direction and information on the second direction may beindependently signaled.

FIG. 22 is a diagram illustrating an exemplary prediction method foracase in which a current block is divided into sub-blocks.

Referring to FIG. 22, a current block is divided into 16 sub-blocks. Inthis case, intra prediction based on a lower right reconstructedreference sample is performed on a sub-block basis. In this case, theintra predictions for each of the sub-blocks can be performed inparallel.

When performing the representative sample-based intra prediction, theresidual signal of the current block may not be encoded/decoded. Forexample, a prediction sample generated through the representativesample-based prediction is determined as a reconstruction sample of thecurrent block.

Whether or not the representative sample-based intra prediction isperformed may be determined in a step of deriving the intra predictionmode. For example, a flag may be transmitted to determine whether toperform a representative sample-based intra prediction on the currentblock. For example, the representative sample-based intra predictionmode can be derived as one of the non-directional modes.

When performing intra or inter prediction, a first color component mayundergo intra prediction and a second color component may undergo interprediction. For example, the first color component is a luminancecomponent, and the second color component is a chrominance component.Conversely, the first color component may be a chrominance component andthe second color component may be a luminance component.

Regarding application of filtering to the prediction samples, whether toapply filtering or not may be determined depending on at least one ofthe intra prediction mode, size (width and height), block shape,multiple sample line-based prediction, and color component of thecurrent block. The filtering refers to a method of filtering one or moreprediction samples using one or more reference samples.

For example, when the intra prediction mode of the current block is apredetermined mode, the filtering may be applied to the predictionsamples. For example, the predetermined mode is a directional mode, anon-directional, a horizontal mode, or a vertical mode.

For example, when the size of the current block falls within apredetermined size range, the filtering may be applied to the predictionsamples. For example, when the current block has a width less than 64and a height less than 64, the filtering may be applied. Alternatively,when the width or height of the current block is larger or smaller thana predetermined size, the filtering may be applied.

For example, whether to apply filtering to the prediction samples may bedetermined depending on the reference sample line used for theprediction. For example, when the reference sample line used for theprediction is the first reference sample line adjacent to the currentblock, the filtering may be applied. On the other hand, when thereference sample line is one of the second and onward reference samplelines positioned around the current block, the filtering may not beapplied. The indicator mrl_index may be used to determine the referencesample line. For example, when the index for the current block is zero,the filtering is applied. However, when the index for the current blockis a value greater than zero, the filtering is not applied.

For example, when the color component of the block element is aluminance signal, the filtering is applied. However, when the colorcomponent of the current block is a chrominance signal, the filtering isnot applied.

The prediction for the current block can be performed by combining oneor more exemplary prediction methods described above.

For example, the prediction for the current block may be performed bycalculating the weighted sum of a prediction value obtained using apredetermined non-directional intra prediction mode and a predictionvalue obtained using a predetermined directional intra prediction mode.In this case, the weights may vary depending on at least one of theintra prediction mode of the current block, the size/shape of thecurrent block, and the position of the prediction target sample.

For example, the prediction for the current may be performed bycalculating the weighted sum of a prediction value obtained using apredetermined intra prediction mode and a prediction value obtainedpredicted using a predetermined inter prediction mode. In this case, theweights may vary depending on at least one of the encoding mode, theintra prediction mode, the inter prediction mode, and the size/shape ofthe current block. For example, when the intra prediction mode is anon-directional mode such as DC or Planar, a weight corresponding to ½may be applied to an intra prediction sample and an inter predictionsample, respectively. Alternatively, when the intra prediction mode is avertical mode, the weight for the intra prediction sample decreases withdistance from the reference sample line above the current block.Similarly, when the intra prediction mode is a horizontal mode, theweight for the intra prediction sample decreases with distance from thereference sample line on the left side of the current block. The sum ofthe weight applied to the intra prediction sample and the weight appliedto the inter prediction sample may be any one of the powers of two. Thatis, it may be any of 4, 8, 16, 32, and so forth. For example, when thesize of the current block is within a predetermined size range, a weightcorresponding to ½ may be applied to the intra prediction sample and theinter prediction sample, respectively.

The intra prediction mode may be fixed to DC mode and Planar mode, ormay be determined through signaling of information. Alternatively, theintra prediction mode may be any mode selected from among MPM candidatemodes, and may be determined through The MPM candidate modes are derivedfrom the intra prediction modes of neighboring blocks. The mode of theneighboring block can be replaced with a predetermined representativemode. For example, the intra prediction mode of a neighboring block is adirectional mode of a specific direction categorized into a verticaldirection group, the mode of the neighboring block is replaced with thevertical mode. On the other hand, when the intra prediction mode of aneighboring block is a directional mode of a specific directioncategorized into a horizontal direction group, the mode of theneighboring block is replaced with the horizontal mode.

The inter prediction may be at least one of DC mode, merge mode, andAMVP mode. When the inter prediction mode of the current block is mergemode, the prediction for the current block may be performed bycalculating the weighted sum of the inter prediction value obtained byusing motion information corresponding to a merge index and theprediction value obtained by using DC or Planar mode.

For example, the prediction for the current block may be performed bycalculating the weighted sum of one or more prediction samples obtainedby using multiple sample lines. For example, the prediction may beperformed by calculating the weighted sum of a first prediction valueobtained by using the first reference sample line near the current blockand a second prediction value obtained by using the second and onwardreference sample lines near the current block. The reference samplelines used to obtain the second prediction value may be reference samplelines indicated by mrl_index. The weights for the first prediction valueand the second prediction value may be equal. Alternatively, the weightsfor the first prediction value and the second prediction value may varydepending on at least one of the intra prediction mode of the currentblock, the size/shape of the current block, and the position of thesample to be prediction. The first prediction value may be a valuepredicted using a predetermined mode. For example, the first predictionvalue may be a value predicted using at least one of DC mode and Planarmode. The second prediction value may be a value predicted using theintra prediction mode of the current block, which is derived in theavailable intra prediction mode derivation step.

When prediction is performed by calculating the weighted sum of one ormore prediction samples, filtering may not be performed on theprediction samples.

The above embodiments may be performed in the same method in an encoderand a decoder.

A sequence of applying to above embodiment may be different between anencoder and a decoder, or the sequence applying to above embodiment maybe the same in the encoder and the decoder.

The above embodiment may be performed on each luma signal and chromasignal, or the above embodiment may be identically performed on luma andchroma signals.

A block form to which the above embodiments of the present invention areapplied may have a square form or a non-square form.

The above embodiment of the present invention may be applied dependingon a size of at least one of a coding block, a prediction block, atransform block, a block, a current block, a coding unit, a predictionunit, a transform unit, a unit, and a current unit. Herein, the size maybe defined as a minimum size or maximum size or both so that the aboveembodiments are applied, or may be defined as a fixed size to which theabove embodiment is applied. In addition, in the above embodiments, afirst embodiment may be applied to a first size, and a second embodimentmay be applied to a second size. In other words, the above embodimentsmay be applied in combination depending on a size. In addition, theabove embodiments may be applied when a size is equal to or greater thata minimum size and equal to or smaller than a maximum size. In otherwords, the above embodiments may be applied when a block size isincluded within a certain range.

For example, the above embodiments may be applied when a size of currentblock is 8×8 or greater. For example, the above embodiments may beapplied when a size of current block is 4×4 or greater. For example, theabove embodiments may be applied when a size of current block is equalto or less than 16×16. For example, the above embodiments may be appliedwhen a size of current block is equal to or greater than 16×16 and equalto or smaller than 64×64.

The above embodiments of the present invention may be applied dependingon a temporal layer. In order to identify a temporal layer to which theabove embodiments may be applied, an additional identifier may besignaled, and the above embodiments may be applied to a specifiedtemporal layer identified by the corresponding identifier. Herein, theidentifier may be defined as the lowest layer or the highest layer orboth to which the above embodiment may be applied, or may be defined toindicate a specific layer to which the embodiment is applied. Inaddition, a fixed temporal layer to which the embodiment is applied maybe defined.

For example, the above embodiments may be applied when a temporal layerof a current image is the lowest layer. For example, the aboveembodiments may be applied when a temporal layer identifier of a currentimage is 1. For example, the above embodiments may be applied when atemporal layer of a current image is the highest layer.

A slice type to which the above embodiments of the present invention areapplied may be defined, and the above embodiments may be applieddepending on the corresponding slice type.

In the above-described embodiments, the methods are described based onthe flowcharts with a series of steps or units, but the presentinvention is not limited to the order of the steps, and rather, somesteps may be performed simultaneously or in different order with othersteps. In addition, it should be appreciated by one of ordinary skill inthe art that the steps in the flowcharts do not exclude each other andthat other steps may be added to the flowcharts or some of the steps maybe deleted from the flowcharts without influencing the scope of thepresent invention.

The embodiments include various aspects of examples. All possiblecombinations for various aspects may not be described, but those skilledin the art will be able to recognize different combinations.Accordingly, the present invention may include all replacements,modifications, and changes within the scope of the claims.

The embodiments of the present invention may be implemented in a form ofprogram instructions, which are executable by various computercomponents, and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include stand-alone or acombination of program instructions, data files, data structures, etc.The program instructions recorded in the computer-readable recordingmedium may be specially designed and constructed for the presentinvention, or well-known to a person of ordinary skilled in computersoftware technology field. Examples of the computer-readable recordingmedium include magnetic recording media such as hard disks, floppydisks, and magnetic tapes; optical data storage media such as CD-ROMs orDVD-ROMs; magneto-optimum media such as floptical disks; and hardwaredevices, such as read-only memory (ROM), random-access memory (RAM),flash memory, etc., which are particularly structured to store andimplement the program instruction. Examples of the program instructionsinclude not only a mechanical language code formatted by a compiler butalso a high level language code that may be implemented by a computerusing an interpreter. The hardware devices may be configured to beoperated by one or more software modules or vice versa to conduct theprocesses according to the present invention.

Although the present invention has been described in terms of specificitems such as detailed elements as well as the limited embodiments andthe drawings, they are only provided to help more general understandingof the invention, and the present invention is not limited to the aboveembodiments. It will be appreciated by those skilled in the art to whichthe present invention pertains that various modifications and changesmay be made from the above description.

Therefore, the spirit of the present invention shall not be limited tothe above-described embodiments, and the entire scope of the appendedclaims and their equivalents will fall within the scope and spirit ofthe invention.

INDUSTRIAL APPLICABILITY

The present invention may be used in encoding/decoding an image.

1. An image decoding method performed by an image decoding apparatus,the method comprising: determining an intra prediction mode of a currentblock; configuring a reference sample for intra prediction of thecurrent block by selecting a reference sample line among a plurality ofreference sample lines adjacent to the current block; generating anintra-predicted block of the current block by performing intraprediction for the current block based on the intra prediction mode andthe reference sample; determining whether to perform filtering theintra-predicted block based on the reference sample line; and filteringthe intra-predicted block based on whether to perform filtering.
 2. Themethod of claim 1, wherein the determining the intra prediction mode ofthe current block comprises: determining whether or not the referencesample line used for configuring the reference sample is a firstreference sample line adjacent to the current block among the pluralityof reference sample lines; and parsing, from a bitstream, an MPM flagindicating whether or not the intra prediction mode of the current blockis identical to at least one among a plurality of intra prediction modecandidates included in an MPM list in case the reference sample line isdetermined to be the first reference sample line.
 3. The method of claim1, wherein the reference sample line is selected based on whether anupper boundary of the current block corresponds to a boundary of acoding tree block.
 4. The method of claim 3, wherein, when the upperboundary of the current block corresponds to the boundary of the codingtree block, a first reference sample line adjacent to the current blockamong the plurality of reference sample lines is selected as thereference sample line.
 5. The method of claim 1, wherein whether toperform filtering the intra-predicted block is determined based on atleast one of a size of the current block or the intra prediction mode ofthe current block, or combinations thereof.
 6. The method of claim 1,wherein the filtering of the intra-predicted block is performed in casethe reference sample line is adjacent to the current block among theplurality of reference sample lines.
 7. The method of claim 1, whereinthe configuring the reference sample comprises: filtering the referencesample in response to that the selected reference sample line is a firstreference sample line adjacent to the current block.
 8. An imageencoding method performed by an image encoding apparatus, the methodcomprising: determining an intra prediction mode of a current block;configuring a reference sample of intra prediction for the current blockby selecting a reference sample line among a plurality of referencesample lines adjacent to the current block; generating anintra-predicted block of the current block by performing intraprediction for the current block based on the intra prediction mode andthe reference sample; determining whether to perform filtering theintra-predicted block based on the reference sample line; and filteringthe intra-predicted block based on whether to perform filtering.
 9. Themethod of claim 8, wherein the determining the intra prediction mode ofthe current block comprises: determining whether or not the referencesample line used for configuring the reference sample is a firstreference sample line adjacent to the current block among the pluralityof reference sample lines; and encoding an MPM flag indicating whetheror not the intra prediction mode of the current block is identical to atleast one among a plurality of intra prediction mode candidates includedin an MPM list in case the reference sample line is determined to be thefirst reference sample line.
 10. The method of claim 8, wherein thereference sample line is selected based on whether an upper boundary ofthe current block corresponds to a boundary of a coding tree block. 11.The method of claim 10, wherein, when the upper boundary of the currentblock corresponds to the boundary of the coding tree block, a firstreference sample line adjacent to the current block among the pluralityof reference sample lines is selected as the reference sample line. 12.The method of claim 8, wherein whether to perform filtering theintra-predicted block is determined based on at least one of a size ofthe current block or the intra prediction mode of the current block, orcombinations thereof.
 13. The method of claim 8, wherein the filteringof the intra-predicted block is performed in case the reference sampleline is adjacent to the current block among the plurality of referencesample lines.
 14. The method of claim 8, wherein the configuring thereference sample comprises: filtering the reference sample in responseto that the selected reference sample line is a first reference sampleline adjacent to the current block.
 15. A non-transitorycomputer-readable recording medium storing a bitstream which isgenerated by an image encoding method, wherein the image encoding methodcomprises: determining an intra prediction mode of a current block;configuring a reference sample for intra prediction of the current blockby selecting a reference sample line among a plurality of referencesample lines adjacent to the current block; generating anintra-predicted block of the current block by performing intraprediction for the current block based on the intra prediction mode andthe reference sample; determining whether to perform filtering theintra-predicted block based on the reference sample line; and filteringthe intra-predicted block based on whether to perform filtering.